Changes needed for ColumnStore and insert cache

MCOL-3875 Columnstore write cache

The main change is to change thr_lock function get_status to
return a value that indicates we have to abort the lock.

Other thing:
- Made start_bulk_insert() and end_bulk_insert() protected so that the
  insert cache can use these

include/thr_lock.h

@@ -126,7 +126,7 @@ typedef struct st_thr_lock {
   /* write_lock_count is incremented for write locks and reset on read locks */
   ulong write_lock_count;
   uint read_no_write_count;
-  void (*get_status)(void*, my_bool);	/* When one gets a lock */
+  my_bool (*get_status)(void*, my_bool);/* Called when one gets a lock */
   void (*copy_status)(void*,void*);
   void (*update_status)(void*);		/* Before release of write */
   void (*restore_status)(void*);        /* Before release of read */