[gtk-osx-users] Removal of support for obsolete MacOS X Versions and global module update.

[John Ralls <jralls ceridwen us>]

I've completed the removal of support for versions of MacOS X earlier than 10.8 from gtk-osx. If you still 
need to build for 10.4u or 10.5, or on 10.4-10.7, I've tagged the last commit that supports that with 
"Last-Lion" to make it easy to have a jhbuildrc and modulesets to support your needs.

I've also gone through all of the modulesets and updated everything. I've tested most of the modules with 
macosx-version-min=10.9 on Sierra with Xcode 8.3. I set up an ElCap test machine with command-line tools and 
noted a few problems, so I'll have a follow-on commit to get that working in a day or two.

Regards,
John Ralls