Fix overlapping replacements in clang-tidy.

Summary: Prevent clang-tidy from applying fixes to errors that overlap with other errors' fixes, with one exception: if one fix is completely contained inside another one, then we can apply the big one.

Reviewers: bkramer, klimek

Subscribers: djasper, cfe-commits, alexfh

Differential Revision: http://reviews.llvm.org/D13516

llvm-svn: 250509