Add support for 'CXFile' (<rdar://problem/7303360>).

- 4 new functions (clang_getCursorSourceFile, clang_getDeclSourceFile, clang_getFileName, clang_getFileTime).

- Should remove clang_getDeclSource() and clang_getCursorSource(). For now, just put 'deprecate' comment in header. 

- Also changed CXX style comment to C style (to eliminate warning).

llvm-svn: 85238