crash if referencing a table" and several other related bugs.
Fix for bug #11834 "Re-execution of prepared statement with dropped function
crashes server." which was spotted during work on previous bugs.

Also couple of nice cleanups:
- Replaced two separate hashes for stored routines used by statement with one.
- Now instead of doing one pass through all routines used in statement for
  caching them and then doing another pass for adding their tables to table
  list, we do only one pass during which do both things.


mysql-test/r/sp-error.result:
  Added test for bug #11834 "Re-execution of prepared statement with dropped
  function crashes server" also covering handling of prepared statements
  which use stored functions but does not require prelocking.
mysql-test/r/sp.result:
  Updated test for LOCK TABLES with views in table list.
  (Old version of statement used in this test will work ok now, since prelocking
   algorithm was tuned and will lock only one multi-set of tables for each routine
   even if this routine is used in several different views).
mysql-test/r/trigger.result:
  Added several tests for triggers using tables.
mysql-test/t/sp-error.test:
  Added test for bug #11834 "Re-execution of prepared statement with dropped
  function crashes server" also covering handling of prepared statements
  which use stored functions but does not require prelocking.
mysql-test/t/sp.test:
  Updated comment about recursive views to reflect current situation.
  Updated test for LOCK TABLES with views in table list.
  (Old version of statement used in this test will work ok now, since prelocking
   algorithm was tuned and will lock only one multi-set of tables for each routine
   even if this routine is used in several different views).
mysql-test/t/trigger.test:
  Added several tests for triggers using tables.
sql/item_func.cc:
  Item_func_sp::cleanup():
    By next statement execution stored function can be dropped or altered so
    we can't assume that sp_head object for it will be still valid.
sql/sp.cc:
  - Added Sroutine_hash_entry structure that represents element in the set of
    stored routines used by statement or routine. We can't as before use
    LEX_STRING for this purprose because we want link all elements of this set
    in list.
  - Replaced sp_add_to_hash() with sp_add_used_routine() which takes into account
    that now we use one hash for stored routines used by statement instead of two
    and which mantains list linking all elelemnts in this hash.
  - Renamed sp_merge_hash() to sp_update_sp_used_routines().
  - Introduced sp_update_stmt_used_routines() for adding elements to the set of
    routines used by statement from another similar set for statement or routine.
    This function will also mantain list linking elements of destination set.
  - Now instead of one sp_cache_routines() function we have family of 
    sp_cache_routines_and_add_tables() functions which are also responsible for
    adding tables used by routines being cached to statement table list. Nice
    optimization - thanks to list linking all elements in the hash of routines
    used by statement we don't need to perform several iterations over this hash
    (as it was before in cases when we have added new elements to it).
sql/sp.h:
  Added declarations of functions used for manipulations with set (hash) of stored
  routines used by statement.
sql/sp_head.cc:
  sp_name::init_qname():
    Now sp_name also holds key identifying routine in the set (hash) of
    stored routines used by statement. 
  sp_head:
    Instead of two separate hashes sp_funs/m_spprocs representing sets of stored
    routines used by this routine we use one hash - m_sroutines. 
  sp_instr_set_trigger_field:
    Added support for subqueries in assignments to row accessors in triggers.
  Removed definition of sp_add_sp_tables_to_table_list() and auxilary functions 
  since now we don't have separate stage on which we add tables used by routines
  used by statement to table list for prelocking. We do it on the same stage as
  we load those routines in SP cache. So all this functionality moved to
  sp_cache_routines_and_add_tables() family of functions.
sql/sp_head.h:
  sp_name:
    Now this class also holds key identifying routine in the set (hash) of stored
    routines used by statement. 
  sp_head:
    Instead of two separate hashes sp_funs/m_spprocs representing sets of stored
    routines used by this routine we use one hash - m_sroutines. 
  sp_instr_set_trigger_field:
    Added support for subqueries in assignments to row accessors in triggers.
  Removed declaration of sp_add_sp_tables_to_table_list() since now we don't have
  separate stage on which we add tables used by routines used by statement to
  table list for prelocking. We do it on the same stage as we load those routines
  in SP cache.
sql/sql_base.cc:
  open_tables():
  - LEX::spfuns/spprocs hashes were replaced with one LEX::sroutines hash.
  - Now instead of doing one pass through all routines used in statement for
    caching them and then doing another pass for adding their tables to table
    list, we do only one pass during which do both things. It is easy to do
    since all routines in the set of routines used by statement are linked in
    the list. This also allows us to calculate table list for prelocking more
    precisely.
  - Now triggers properly inform prelocking algorithm about tables they use.
sql/sql_lex.cc:
  lex_start():
    Replaced LEX::spfuns/spprocs with with one LEX::sroutines hash.
    Added LEX::sroutines_list list linking all elements in this hash.
  st_lex::st_lex():
    Moved definition of LEX constructor to sql_lex.cc file to be able
    use sp_sroutine_key declaration from sp.h in it.
sql/sql_lex.h:
  LEX:
    Replaced two separate hashes for stored routines used by statement with one.
    Added list linking all elements in this hash to be able to iterate through all
    elements and add new elements to this hash at the same time.
    Moved constructor definition to sql_lex.cc.
sql/sql_parse.cc:
  mysql_execute_command():
    Replaced LEX::spfuns/spprocs with one LEX::sroutines hash.
sql/sql_trigger.cc:
  Added missing GNU GPL notice.
  Table_triggers_list::check_n_load()
    Added initialization of sroutines_key which stores key representing
    triggers of this table in the set (hash) of routines used by this statement.
sql/sql_trigger.h:
  Added missing GNU GPL notice.
  Table_triggers_list:
    Added sroutines_key member to store key representing triggers of this
    table in the set (hash) of routines used by this statement.
    Declared sp_cache_routines_and_add_tables_for_triggers() as friend since
    it needs access to sroutines_key and trigger bodies.
sql/sql_yacc.yy:
  - Now we use sp_add_used_routine() instead of sp_add_to_hash() for adding
    elements to the set of stored routines used in statement.
  - Enabled support of subqueries as right sides in assignments to triggers' row
    accessors.