Sync with upstream ffa3961 (svn revision 360359):
ffa3961: Fix a bug with dirty file system handling.
r356313 broke handling of dirty file system because we have restricted
the correction of "odd" byte sequences to checkfat(), and as a result
the dirty bit is never cleared. The old fsck_msdosfs code would write
FAT twice to fix the dirty bit, which is also not ideal.
Fix this by introducing a new rountine, cleardirty() which will perform
the set of clean bit only, and use it in checkfilesys() if we thought
the file system was dirty.
996c6ae: Use humanize_number to format available and bad space sizes.
(Visible change is the addition of KiB suffix in fsck_msdos summary
on Android as we don't currently have humanize_number which supports
28bbeac: Diff reduction against NetBSD, no functional change.