led to creating corrupted index.

Corrected fix. The new method called prepare2 is added to the select_create
class. As all preparations are done by the select_create::prepare function
it doesn't do anything. Slightly changed algorithm of calling the 
start_bulk_insert function. Now it's called from the select_insert::prepare2
function when the SQL_BUFFER_RESULT flags is set.
The is_bulk_insert_mode flag is removed as it is not needed anymore.