Make vim also output a helpful message in some error cases.
Make vim also output a helpful message in some error cases.

When clang-format encounters a syntax error, it will not format that
line; we're now using the same mechanism we're already using in emacs to
show a helpful error message to the user.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@238823 91177308-0d34-0410-b5e6-96231b3b80d8

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