Introducing new tool clang-replace

Introducing new tool 'clang-replace' that finds files containing
serialized Replacements and applies those changes after deduplication
and detecting conflicts.

Currently the tool does not apply changes. It stops just after the
deduplication and conflict report phase. Forthcoming patches will
complete functionality.

Both build systems updated for new tool.

Includes a conflict test case.

clang-replace added to Doxygen build.

Differential Revision: http://llvm-reviews.chandlerc.com/D1424

llvm-svn: 189008