Add some comments to TypoCorrectionConsumer.
Add some comments to TypoCorrectionConsumer.

Also move the constructor for NamespaceSpecifierSet out of line to
improve the class' readability. I meant to do these two things while
cleaning up the previous TypoCorrectionConsumer changes and have them
folded into those changes.

No functionality changed.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@210686 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang