bindings: expose diagnostic formatting to Python
bindings: expose diagnostic formatting to Python

This makes it easier for tools using the Python libclang bindings to display
diagnostics in a manner consistent with clang.

Patch by Omar Sandoval!

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@278315 91177308-0d34-0410-b5e6-96231b3b80d8

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