Added error checking for errors when attempting to use stored procedures
  after the mysql.proc table has been dropped, corrupted, or tampered with.
  Test cases were put in a separate file (sp-destruct.test).


mysql-test/t/sp.test:
  Added comment.
sql/share/errmsg.txt:
  New error message for corrupted mysql.proc table.
sql/sp.cc:
  Check and return error code when caching stored routines.
  In the case when no error message has been set, set one.
sql/sp.h:
  Return error code from stored routine cache function.
sql/sql_base.cc:
  Check for error from sp_cache_routines_* calls.
sql/sql_trigger.h:
  Updated friend declaration for sp_cache_routines*.
mysql-test/r/sp-destruct.result:
  New test file for destruction of the mysql.proc table.
mysql-test/t/sp-destruct.test:
  New result file for destruction of the mysql.proc table.