* Many fixes for \brief summaries (adding some, and making others shorter);
* Don't try to explicit tell Doxygen a namespace name (and particularly
  don't get it wrong);
* Typo fix: instantitions -> instantiations;
* Slightly more use of \pre for documenting preconditions.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158852 91177308-0d34-0410-b5e6-96231b3b80d8