binlogging of insert into a autoincrement blackhole table ignored
an explicit set insert_id.

Fixed with refining of the blackhole's insert method to call
update_auto_increment() that prepares binlogging the insert query 
with the preceeding set insert_id.

Note, as the engine does not store any actual data one has to explicitly
provide to the server with the value of the autoincrement column via
set insert_id. Otherwise binlogging will happend with the default 
set insert_id=1.


mysql-test/r/blackhole.result:
  results changed
mysql-test/t/blackhole.test:
  a regression test for the bug added
sql/ha_blackhole.cc:
  blackhole's insert method is refined to call update_auto_increment()
  that prepares binlogging the insert query with the preceeding set insert_id.