******
This patch fixes the following bugs:
  - Bug#5889: Exit handler for a warning doesn't hide the warning in
    trigger
  - Bug#9857: Stored procedures: handler for sqlwarning ignored
  - Bug#23032: Handlers declared in a SP do not handle warnings generated
    in sub-SP
  - Bug#36185: Incorrect precedence for warning and exception handlers

The problem was in the way warnings/errors during stored routine execution
were handled. Prior to this patch the logic was as follows:

  - when a warning/an error happens: if we're executing a stored routine,
    and there is a handler for that warning/error, remember the handler,
    ignore the warning/error and continue execution.

  - after a stored routine instruction is executed: check for a remembered
    handler and activate one (if any).

This logic caused several problems:

  - if one instruction generates several warnings (errors) it's impossible
    to choose the right handler -- a handler for the first generated
    condition was chosen and remembered for activation.

  - mess with handling conditions in scopes different from the current one.

  - not putting generated warnings/errors into Warning Info (Diagnostic
    Area) is against The Standard.

The patch changes the logic as follows:

  - Diagnostic Area is cleared on the beginning of each statement that
    either is able to generate warnings, or is able to work with tables.

  - at the end of a stored routine instruction, Diagnostic Area is left
    intact.

  - Diagnostic Area is checked after each stored routine instruction. If
    an instruction generates several condition, it's now possible to take a
    look at all of them and determine an appropriate handler.

mysql-test/r/signal.result:
  Update result file:
    1. handled conditions are not cleared any more;
    2. reflect changes in signal.test
mysql-test/r/signal_demo3.result:
  Update result file: handled conditions are not cleared any more.
  Due to playing with max_error_count, resulting warning lists
  have changed.
mysql-test/r/sp-big.result:
  Update result file: handled conditions are not cleared any more.
mysql-test/r/sp-bugs.result:
  Update result file: handled conditions are not cleared any more.
mysql-test/r/sp-code.result:
  Update result file:
    1. handled conditions are not cleared any more.
    2. add result for a new test case in sp-code.test.
mysql-test/r/sp-error.result:
  Update result file:
    1. handled conditions are not cleared any more.
    2. add result for a new test case in sp-error.test.
mysql-test/r/sp.result:
  Update result file: handled conditions are not cleared any more.
mysql-test/r/sp_trans.result:
  Update result file: handled conditions are not cleared any more.
mysql-test/r/strict.result:
  Update result file: handled conditions are not cleared any more.
mysql-test/r/view.result:
  Update result file: handled conditions are not cleared any more.
mysql-test/suite/funcs_1/r/innodb_storedproc_02.result:
  Update result file: handled conditions are not cleared any more.
mysql-test/suite/funcs_1/r/memory_storedproc_02.result:
  Update result file: handled conditions are not cleared any more.
mysql-test/suite/funcs_1/r/myisam_storedproc_02.result:
  Update result file: handled conditions are not cleared any more.
mysql-test/suite/funcs_1/r/storedproc.result:
  Update result file: handled conditions are not cleared any more.
mysql-test/suite/rpl/r/rpl_row_sp005.result:
  Update result file: handled conditions are not cleared any more.
mysql-test/suite/rpl/r/rpl_row_sp006_InnoDB.result:
  Update result file: handled conditions are not cleared any more.
mysql-test/suite/rpl/r/rpl_row_trig003.result:
  Update result file: handled conditions are not cleared any more.
mysql-test/t/signal.test:
  Make a test case more readable in the result file.
mysql-test/t/sp-code.test:
  Add a test case for Bug#23032 checking that
  No Data takes precedence on Warning.
mysql-test/t/sp-error.test:
  Adding test cases for:
    - Bug#23032
    - Bug#36185
    - Bug#5889
    - Bug#9857
mysql-test/t/sp.test:
  Fixing test case to reflect behavioral changes made by the patch.
sql/sp_head.cc:
  Reset the per-statement warning count before executing
  a stored procedure instruction.
  
  Move to a separate function code which checks the
  completion status of the executed statement and searches
  for a handler.
  
  Remove redundant code now that search for a handler is
  done after execution, errors are always pushed.
sql/sp_pcontext.h:
  Remove unused code.
sql/sp_rcontext.cc:
  - Polish sp_rcontext::find_handler(): use sp_rcontext::m_hfound instead
    of an extra local variable;
  
  - Remove sp_rcontext::handle_condition();
  
  - Introduce sp_rcontext::activate_handler(), which prepares
    previously found handler for execution.
  
  - Move sp_rcontext::enter_handler() code into activate_handler(),
    because enter_handler() is used only from there;
  
  - Cleanups;
  
  - Introduce DBUG_EXECUTE_IF() for a test case in sp-code.test
sql/sp_rcontext.h:
  - Remove unused code
  - Cleanups
sql/sql_class.cc:
  Merge THD::raise_condition_no_handler() into THD::raise_condition().
  After the patch raise_condition_no_handler() was called
  in raise_condition() only.
sql/sql_class.h:
  Remove raise_condition_no_handler().
sql/sql_error.cc:
  Remove Warning_info::reserve_space() -- handled conditions are not
  cleared any more, so there is no need for RESIGNAL to re-push them.
sql/sql_error.h:
  Remove Warning_info::reserve_space().
sql/sql_signal.cc:
  Handled conditions are not cleared any more,
  so there is no need for RESIGNAL to re-push them.