create diff only if content changed

Diffs just make sense if there is actually a diff.
So just update the post if content is unchanged, else
create a new version of the post for diffing.
detect contenttype by checking snippet title

Now its quite easy to set the content type to
use a reasonable fileextension in the snippet
title.
use the postid to differ the likes/dislikes

When clicking like/dislike on the index-view the data
was updatet for all divs with likesize/dislikesize.
Now just the div with the correct post id gets updated.
Merge pull request #21 from darinkes/diff

create diff only if content changed
Merge pull request #18 from darinkes/js2filename

detect contenttype by checking snippet title
Merge pull request #23 from darinkes/likedislike-fixes

use the postid to differ the likes/dislikes