* remove get_next_init and move its functionality to QUICK_RANGE_SELECT::reset()
 * added more comments
 * added empty FT_SELECT::reset() 


sql/opt_range.cc:
  Post WL#2126 fixes: remove get_next_init and move its functionality to QUICK_RANGE_SELECT::reset()
  Add needed error checks since QUICK_RANGE_SELECT::reset can fail now.
sql/opt_range.h:
  Post WL#2126 fixes: 
   * remove get_next_init and move its functionality to QUICK_RANGE_SELECT::reset()
   * added more comments
   * added empty FT_SELECT::reset() since QUICK_RANGE_SELECT::reset() it was using wasn't doing anything useful.
sql/records.cc:
  Post WL#2126 fixes: 
   * remove redundant get_next_init call