HAMMER 43C/Many: Performance cleanup
* Do not put an inode on the sync list when it becomes inactive, unless
it no longer has filesystem visibility. This greatly reduces the amount
of cycling which occurs on the inode B-Tree element, and greatly reduces
spurious backend flushes.
This change results in a major performance improvement for both reads
and writes in a massively parallel I/O test (blogbench). Write
performance more then doubles and read performance increases by 20%.
* Lock the freemap free code.
* Remove some of the debug code.