[PATCH] Add CommentOptions, allow specifying custom comment block commands

[Ben Gertzfield]

  Thanks again. I updated ##CommentLexer## and ##CommentParser## to include the new parameters in the PCH.

  I'm not sure how to handle upgrade and downgrade issues; do we assume that PCH file are just discarded between clang versions?

  Anyway, the PCH test seems to still be failing in the same way, as if the option were not being passed through:

  http://llvm-reviews.chandlerc.com/P47
  http://llvm-reviews.chandlerc.com/P48

  Any more tips? Sorry for taking up all your time, I'm just not at all familiar with PCH files and how to debug them.

http://llvm-reviews.chandlerc.com/D272