[SHOW] EXPLAIN UPDATE/DELETE, code re-structuring

- Make query plan be re-saved after the first join execution
  (saving it after JOIN::cleanup is too late because EXPLAIN output 
   is currently produced before that)
- Handle QPF allocation/deallocation for edge cases, like unsuccessful
  BINLOG command.
- Work around the problem with UNION's direct subselects not being visible.
- Update test results ("Using temporary; Using filesort" are now always printed 
  last in the Extra column)
- This cset gets rid of memory leaks/crashes. Some result mismatches still remain.

sql/sql_parse.cc

@@ -4750,8 +4750,14 @@ finish:
     ha_maria::implicit_commit(thd, FALSE);
 #endif
   }
-
   lex->unit.cleanup();
+  //psergey-todo: print EXPLAIN here? After the above JOIN::cleanup calls?
+  // how do we print EXPLAIN extended, then?
+  if (lex->describe)
+  {
+    DBUG_ASSERT(lex->query_plan_footprint);
+    ///..
+  }
   /* Free tables */
   thd_proc_info(thd, "closing tables");
   close_thread_tables(thd);