It's *.* on Windows, but just * on UN*X; add a header that provides the
definition, and use it instead of hardwiring *.*.
Call the entry "All Files", that being the conventional name, rather
than "Any File", whilst we're at it.
Change-Id: I7c29324fc5b41e93c150e1ec67f1529f171dc6a3
Reviewed-on: https://code.wireshark.org/review/14243
Reviewed-by: Guy Harris <guy@alum.mit.edu>