fails if a database is not selected prior.

The problem manifested itself when a user tried to
create a routine that had non-fully-qualified identifiers in its bodies
and there was no current database selected.

This is a regression introduced by the fix for Bug 19022:

The patch for Bug 19022 changes the code to always produce a warning
if we can't resolve the current database in the parser. 
In this case this was not necessary, since even though the produced
parsed tree was incorrect, we never re-use sphead
that was obtained at first parsing of CREATE PROCEDURE.
The sphead that is anyhow used is always obtained through db_load_routine,
and there we change the current database to sphead->m_db before
calling yyparse.

The idea of the fix is to resolve the current database directly using 
lex->sphead->m_db member when parsing a stored routine body, when
such is present.

This patch removes the need to reset the current database
when loading a trigger or routine definition into SP cache.
The redundant code will be removed in 5.1.


mysql-test/r/sp.result:
  Update test results (Bug#29050)
mysql-test/r/trigger.result:
  Update results.
mysql-test/t/sp.test:
  Add a test case for Bug#29050
mysql-test/t/trigger.test:
  Fix wrong behavior covered with tests.
sql/sql_lex.cc:
  Implement st_lex::copy_db_to().
sql/sql_lex.h:
  Declare st_lex::copy_db_to().
sql/sql_parse.cc:
  Use st_lex::copy_db_to() in add_table_to_list, rather than
  THD::copy_db_to(). The former will use the database of the sphead,
  if we're parsing a stored routine, not the default database in
  THD. The default database is needed to initialize tables->db
  when the database part was not explicitly specified in the identifier.
sql/sql_yacc.yy:
  Use st_lex::copy_db_to() in the parser, rather than
  THD::copy_db_to(). The former will use the database of the sphead,
  if we're parsing a stored routine, not the default database in
  THD.