WL#1451: Add log file size limit for automatic flush

Currently in MySQL you need to manually rotate/flush log files if you want to
limit their side. It is not very friendly nether convenient.

We shall have an option for each log file, limiting its maximum size, after
which it gets automatically rotating to -old, removing forer old file.

This will allow you to always have   log_max_size to 2*log_max_size  log data
available.

It is expecially interesting for slow query log and error log which you often
want to be enabled but would not like them to consume all the space.

At the sime time this is done, one should look at fixing BUG#2712:

When issuing a flush command, we should rename the error log with to
hostname.err-old-'datetime' to enable the user to keep a set of logs for
later inspection.