EasyTAG on OS X

[Tony Young <tony rfw name>]

Hi there,

I've written a preliminary set of patches for EasyTAG on OS X and
committed them to GitHub repo: https://github.com/rfw/easytag-mac

It ifdefs some OS X-specific behavior using gtk-osx-integration, so it
should build as usual on other platforms. However, the changes are a
bit messy (particularly how I've ifdeffed <Control> to <Meta> on OS
X). I've also managed to build it with GTK3 with some effort and it
works great.

Let me know what you think! Hopefully there'll be some official builds
of EasyTAG for OS X soon ;)

Cheers,
Tony