dropping/creating tables".

The bug could lead to a crash when multi-delete statements were
prepared and used with temporary tables.

The bug was caused by lack of clean-up of multi-delete tables before
re-execution of a prepared statement. In a statement like
DELETE t1 FROM t1, t2 WHERE ... the first table list (t1) is
moved to lex->auxilliary_table_list and excluded from lex->query_tables
or select_lex->tables. Thus it was unaccessible to reinit_stmt_before_use
and not cleaned up before re-execution of a prepared statement. 


mysql-test/r/ps.result:
  Updated test results (Bug#19399)
mysql-test/t/ps.test:
  A test case for Bug#19399 "Stored Procedures 'Lost Connection' when 
  dropping/creating tables": test that multi-delete
  tables are cleaned up properly before re-execution.
sql/sql_lex.cc:
  Always initialize auxilliary_table_list when we initialize the lex:
  this way we don't have to check that lex->sql_command equals to
  SQLCOM_DELETE_MULTI whenever we need to access auxilliary_table_list.
  In particular, in reinit_stmt_before_use we can simply check that
  auxilliary_table_list is not NULL and clean it up if the check returns
  a true value.
sql/sql_prepare.cc:
  Move the one table clean-up functionality to a method of st_table_list.
  Clean up auxiliary_table_list if it's not empty.
sql/table.cc:
  Implement st_table_list::reinit_before_use().
sql/table.h:
  Declare st_table_list::reinit_before_use().