cindex.py: Avoid deprecated function
cindex.py: Avoid deprecated function

Implement Diagnostic::category_name() using clang_getDiagnosticCategoryText()
instead of the deprected clang_getDiagnosticCategoryName().

Preserves existing behaviour and API covered by existing tests.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@206712 91177308-0d34-0410-b5e6-96231b3b80d8

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