Add a 'dump' method to the type map. Doxygenify some of the comments and add a

Add a 'dump' method to the type map. Doxygenify some of the comments and add a
few comments where none existed before. Also change a function's name to match
the current coding standard.
No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153276 91177308-0d34-0410-b5e6-96231b3b80d8