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
  larger numbers)

28bbeac: Diff reduction against NetBSD, no functional change.

Bug: 155081558
Test: build
Change-Id: I352ad474215fd340399697c0606d69687c8189d1