We binlog the DROP TABLE for each table that was actually dropped. Per Sergei's 
suggestion a fixed buffer for the DROP TABLE query is pre-allocated from THD pool, and 
logging now is done in batches - new batch is started if the buffer becomes full.
Reduced memory usage by reusing the table list instead of accumulating a list of 
dropped table names. Also fixed the problem if the table was not actually dropped, eg
due to permissions. Extended the test case to make sure batched query 
logging does work.