* Make index merge quick selects code allow perform several scans.
 * Delay additional handler objects creation till row retrieval is started.


include/queues.h:
  Added trivial queue_remove_all macro
mysql-test/r/index_merge.result:
  Testcase for BUG#4177
mysql-test/t/index_merge.test:
  Testcase for BUG#4177
sql/opt_range.cc:
  Fix for BUG#4177: 
   * For any quick select, row retrieval can be performed several times. Now all index_merge quick selects code handles such cases properly.
   * In QUICK_INDEX_MERGE_SELECT we use one handler object for all merged scans, and it was possible that in 
      destructor several cleanup functions were called 
   * Additionally
    - Removed redundant QUICK_INDEX_MERGE_SELECT members.
    - Now QUICK_ROR_*_SELECTs create additional handler objects only when row retrieval is started
      So if join optimizer chooses other access method, we don't create/delete handlers.