Disable indent auto-corrections for comment blocks

Languages do not have indent patterns that handle (block) comments, so TextMate basically never does the right thing inside these.

Ideally we would also disable it for the line following the block comment (since the estimated indent there is thrown off by the block comment), but that is presently not possible. Users can disable auto-corrections for the entire file scope, should they run into this a lot.

Closes textmate/textmate#721.