OPTIMIZE TABLE <archive table>

This recompresses the table, thus removing any additional gzip headers caused by opening/closing or flushing the table.


mysql-test/r/archive.result:
  Added optimize test case for archive engine.
mysql-test/t/archive.test:
  Added test case for OPTIMIZE table <archive table>
sql/examples/ha_archive.cc:
  The big change was the addition of optimize() call to allow tables to be recompressed (so if you have been reading/writing/reading/writing and ending up with larger files then you should, this will solve it). Though adding this feature is going to make it a real headache to add row level locking. 
  Also fixed bug reported by JD where storage engine code was not functioning (this of course was because I didn't check for the propper return value for hash_init). Removed BROKEN_GZIP ifdef since there was no way to enable it.
sql/examples/ha_archive.h:
  Added optimize() method.