Shorten the output of `clang-format --version`, include revision number.

Before:
  $ clang-format  --version
  LLVM (http://llvm.org/):
    LLVM version 3.5svn
    Optimized build with assertions.
    Built Jan  3 2014 (14:28:46).
    Default target: x86_64-apple-darwin13.0.0
    Host CPU: core-avx-i

Now:
  $ bin/clang-format --version
  clang-format version 3.5 (198452)

llvm-svn: 198694