PrettyPatch should handle "delta" patch mechanism in git binary patches

PrettyPatch should handle "delta" patch mechanism in git binary patches
https://bugs.webkit.org/show_bug.cgi?id=67628

Git patches are encoded using two mechanisms - "literal" and "delta".
For details of these mechanisms, see the function emit_binary_diff_body
in the git source file diff.c (https://github.com/git/git/blob/master/diff.c).

When determining if a binary file patch is an image or not we should accept
both literal and delta patch encodings.

When reconstructing the images from the patches, if we have a delta patch
we may download the previous revision from svn.webkit.org to get the image data.

Patch by Ben Wells <benwells@chromium.org> on 2011-09-14
Reviewed by Adam Roben.

* PrettyPatch/PrettyPatch.rb:
* PrettyPatch/PrettyPatch_test.rb:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@95159 268f45cc-cd09-0410-ab3c-d52691b4dbfc