[PATCH] Introduce Replacement deduplication and conflict detection function

[Edwin Vane]

  1. I was concerned that although `Range` describes what I want that my use of it to describe an offset and number of consecutive items in a vector was against it's intended use as a **source** range.
  2. Just making sure. When we switch `Replacements` to be an `std::vector` from `std::set` when deduplication happens this new function would be used which is doing something new from before: i.e. conflict detection.
  3. That was the intention.

  So ready to commit?

http://llvm-reviews.chandlerc.com/D1314

BRANCH
  dedup

ARCANIST PROJECT
  clang