Gtk+ win32 fixes, please test

[Alexander Larsson <alexl redhat com>]

I just pushed a bunch of changes to how grabs and crossing events
work in the win32 backend to the gtk-2-24-win32 branch, and I want to
fix any other leftover bugs from the client side windows conversion.

Can any people interested in the win32 code please try this out and
report any issues, regressions against gtk-2-24 or just things that are
broken on windows related to windows and events.

I'm doing this work on the 2.24 branch because gtk2 is what most apps
are still using on win32. When this seems to work well I want to forward
port it to 3.2.