Adding 4 ASTMatchers: typedefDecl, isInMainFile, isInSystemFile, isInFileMatchingName

Summary:
Often one is only interested in matches within the main-file or matches
that are not within a system-header, for which this patch adds
isInMainFile and isInSystemFile. They take no arguments and narrow down
the matches.

The isInFileMatchingName is mainly thought for interactive
clang-query-sessions, to make a matcher more specific without restarting
the session with the files you are interested in for that moment. It
takes a string that will be used as regular-expression to match the
filename of where the matched node is expanded.

Patch by Hendrik von Prince.

llvm-svn: 222646