\file and \brief markup and appear in Doxygen's summaries (and eventually at
http://clang.llvm.org/doxygen/files.html).  Fixed up another couple of minor
glitches in the docs at the same time.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@159517 91177308-0d34-0410-b5e6-96231b3b80d8