Optional add-on to previous patch which corrected logging to file)
wherein we change width of thread-ID field in slow and general log
tables from INT to BIGINT (4 to 8 bytes), for correct logging of
very large thread-IDs.

Thread-IDs can get very large; patch adjusts general-logging
and slow query logging to reflect that and log those IDs correctly.

Backport to 5.6.