also modified check_all function to suppress all warnings since they aren't
relevant to what this test is doing (allows quiet checking of regsub, for
instance)

There are two ways to use this -- as a filter (e.g. using C-U M-| on a
regex string literal in an Emacs buffer) or from a Python program
which imports this as a module.  Read the doc string for more info,
and also some caveats (some cases aren't handled right).