Add self-test for skdiff, and remove date/time from skdiff output so it passes.

BUG=http://code.google.com/p/skia/issues/detail?id=612
Review URL: https://codereview.appspot.com/6198074

git-svn-id: http://skia.googlecode.com/svn/trunk@3938 2bbb7eff-a529-9590-31e7-b0007b416f81
12 files changed