changes in query execution plans.
Fixed by introducing table->rpl_write_set which holds which columns should
be stored in the binary log.

Other things:
- Removed some not needed references to read_set and write_set to make
  code really changing read_set and write_set easier to read
  (in opt_range.cc)
- Added error handling of failed unpack_current_row()
- Added missing call to mark_columns_needed_for_insert() for DELAYED INSERT
- Removed not used functions in_read_set() and in_write_set()
- In rpl_record.cc, removed not used variable error