Fix crash in ha_calpont_impl_close_connection()
Fix leak in ci.tableMap.
Removed extra returns in pushdown_init to avoid crashes.
create_select_handler now detects INSERT..SELECT.
buildConstColFromFilter now uses any kind of filter to supply
relevant columns.
Remove strings used by vtable redo phase.
Make FromSubQuery aware of Pushdown handlers.
Changed debug_walk to work around changed Item framework.
Temporary disabled derived handler and unsupported features checks.
