Work around a gtk+ default window size regression

The gtk+ change b495ce5... introduced a regression w.r.t. to the
default window size handling.

This means the terminal has a size of 1x1 character, which is not very
useful :)

Well, we should not use the default size in the first place, but anyway.

See https://bugzilla.gnome.org/show_bug.cgi?id=696187
Fixed the shell version check

This was meaning that "3.7.92" (3792) was more recent than "3.8.0" (380)
which is not quite the expected behavior.
Cope with the KeyBindingMode move of 3.7.2

Its location changed from Main to Shell and its case changed from
KeybindingMode to KeyBindingMode.
Work around the new frame sync of mutter 3.7.90

I did not investigate the issue fully, but it covers it for the time
being, as this is really bothering when you extensively use the terminal.

Also, bump the supported gnome-shell versions.