glibmm branched for 2.26

[Murray Cumming <murrayc murrayc com>]

I have created the glibmm-2-26 branch to target glib's glib-2-26 branch.
glibmm 2.26 doesn't have Gio::Application, so you'll need to use master
if you want to work with gtkmm 3 (master), which uses it for
Gtk::Application.

I'm not going to worry too much about the glibmm-2-26 branch right now,
because I don't expect to get the new API stable enough for a glibmm
2.26.0 release soon anyway.



-- 
murrayc murrayc com
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