(diff-apply-hunk): Function basically rewritten. Now understands

(diff-apply-hunk):  Function basically rewritten.  Now understands
  non-unified diffs.  Some functionality moved into `diff-hunk-text' and
  `diff-find-text'.  Add OTHER-FILE, DRY-RUN, POPUP, and NOERROR
  arguments.  If DRY-RUN is true, don't actually modify anything.  Only
  reposition point in the patched file if the patch succeeds.  Only pop
  up another window if POPUP is true.  Emit a message describing what
  happened if successful, and at what line-offset.  Automatically detect
  reversed hunks and do something appropriate.
(diff-hunk-text, diff-find-text): New functions.
(diff-filter-lines): Function removed.
(diff-test-hunk): New function.
(diff-goto-source): Rewritten in terms of diff-apply-hunk.