Dropping the table was not the real problem, the problem was with errors
  occuring within error handlers.


mysql-test/r/sp-error.result:
  New test case for BUG#3294.
mysql-test/t/sp-error.test:
  New test case for BUG#3294.
sql/sp_head.cc:
  Use hreturn instruction both for continue and exit handlers (a special case
  of a jump).
sql/sp_head.h:
  Use hreturn instruction both for continue and exit handlers (a special case
  of a jump).
sql/sp_rcontext.cc:
  Keep track on if we're in a handler already, for error handling.
sql/sp_rcontext.h:
  Keep track on if we're in a handler already, for error handling.
sql/sql_yacc.yy:
  Use hreturn instruction both for continue and exit handlers (a special case
  of a jump).