- When an ALTER TABLE RENAME is performed on windows, the files are closed and their cached file 
   descriptors are marked invalid. Performing INSERT, UPDATE or SELECT on the associated merge
   table causes a server crash on windows. This patch adds a test for bad file descriptors when a 
   table attempts a lock. If a bad descriptor is found an error is thrown. An additional FLUSH TABLES
   will be necessary to further operate on the associated merge table.