Octopus merge of the following five patches.

  Update git-apply-patch-script for symbolic links.
  Make git-prune-script executable again.
  Do not write out new index if nothing has changed.
  diff-cache shows differences for unmerged paths without --cache.
  Update diff engine for symlinks stored in the cache.

Signed-off-by: Junio C Hamano <junkio@cox.net>