Provide better emacs integration.

The new emacs integration is simpler, does not save the current file
before reformatting and ensures that emacs does not scroll as a result
of formatting.

Also explicitly set the style in clang-format tests to make them more
robust.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179372 91177308-0d34-0410-b5e6-96231b3b80d8