windows-remove-log-messages-20050826

windows-remove-log-messages-20050826

The log message added to buf_LockedCleanAsync() during the debugging
post 1.3.8201 is output for 1/10th of all buffers once every 5 seconds.
This is a huge performance hit.  Move the message so that it is only
output for buffers that are actually dirty.

Also, change the algorithm so that the sqrt() of the number of buffers
are checked every 5 seconds instead of 1/10th.   This will do a better
job with very large cache sizes.