* fix: unwritten sparse file regions could get corrupted if the end
of a write wasn't aligned to cluster boundary. Sparse files are very
rarely used, most typically by bittorent clients.
* fix: creation of read-only files failed.
* change: free inode calculation was CPU intensive during write activity.
This could reduce write performance when millions of files are used if
a file manager or desktop applet regularly polled for disk space usage.
Now the statfs() system call is constant time.
* change: file creation performance is improved by 40-80%.
* change: smart directory traversal is 20-200% faster for disk based and
300-600% faster for memory cache based traversals.
0be058961a