In the patch for BUG#21842, the code for handling old rows events were
refactored.  There were a bug in the refactored code (possibly introduced
after the patch for BUG#21842) that caused caused the refactored old events
to read a columns bitmap after image even though there is no such bitmap
for old events. As a result, the reading got out of sync, and started reading
invalid data.

This patch removes all trace of the after image column bitmap from the refactored
old events and removes functions that are no longer needed because they are empty. 


sql/log_event.cc:
  Adding debug printouts and adding old rows events names to output
  so that they are not printed as unknown events.
sql/log_event_old.cc:
  Adding debug printouts to see how the old events are partitioned
  when being decoded.  Removing all traces of the column bitmap for
  the after image in the old events since there is none.
  
  Removing the following functions since they are no longer needed:
  - Update_rows_log_event_old::init()
  - Update_rows_log_event_old::~Update_rows_log_event_old()
  
  Removing unused local variable.
sql/log_event_old.h:
  Removing all traces of the column bitmap for the after image in
  the old events since there is none.
  
  Removing the following functions since they are no longer needed:
  - Update_rows_log_event_old::init()
  - Update_rows_log_event_old::is_valid()
  - Update_rows_log_event_old::~Update_rows_log_event_old()
  
  Removing unused local variable.
mysql-test/suite/bugs/r/rpl_bug31583.result:
  New BitKeeper file ``mysql-test/suite/bugs/r/rpl_bug31583.result''
mysql-test/suite/bugs/t/rpl_bug31583.test:
  New BitKeeper file ``mysql-test/suite/bugs/t/rpl_bug31583.test''