[PATCH] rewrite-includes: Rewrite __has_include(_next) to get rid of a host dependency.

[David Blaikie]

  Looks reasonable to me (though I haven't applied/tested it)

  Did you want to add any negative test cases for mangled inputs (something to hit 261 and/or 276)?

  Sorry for the delay.

http://llvm-reviews.chandlerc.com/D594

BRANCH
  master

ARCANIST PROJECT
  clang