Pull predecessor and successor iterators out of the CFG*.h files, and plop them into

Pull predecessor and successor iterators out of the CFG*.h files, and plop them into
the BasicBlock class where they should be.  pred_begin/pred_end become methods on BasicBlock,
and the cfg namespace isn't used anymore.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@691 91177308-0d34-0410-b5e6-96231b3b80d8