Avoid column limit violation in block comments in certain cases.

Summary:
Add penalty when an excessively long line in a block comment can not be
broken on a leading whitespace. Lack of this addition can lead to severe column
width violations when they can be easily avoided.

Reviewers: djasper

Reviewed By: djasper

CC: cfe-commits, klimek

Differential Revision: http://llvm-reviews.chandlerc.com/D1071

llvm-svn: 185337