[PATCH 0 of 2 RFC] Platform-specific merge tools

[Dan Villiom Podlaski Christiansen]

Hi,

The first patch in this series is relatively uncontroversial; it adds
a pure fallback for osutil.isgui() on Mac OS X.

The second patch is more ambitious, and thus more likely to be
horribly wrong: it allows merge tools to specify which type of GUI
they require. I've tested it on my Mac and it seems to work as
expected, but more testing would be nice.

--

- Dan