HiDPI stuff partially merged

[Alexander Larsson <alexl redhat com>]

I just merged the wip/window-scales2 branch. This means that gtk+ master
has some level of support for window scaling. 

If you want to test this, you will still need the cairo branch at:
http://cgit.freedesktop.org/~ickle/cairo/log/?h=device-scale
(It still builds without it, but doesn't support scaling)

Chris will merge this into cairo master and start a 1.13 version as soon
as he manages to release the latest 1.12.x version, then this will not
be needed. (Also, Chris talked about making cairo automatically inherit
device-scale in cairo_surface_create_similar, if that happens we need to
modify gdk_window_create_similar_surface to not do this.)

I also have some patches to add automatic detection of hidpi screens and
enable the scale at:
https://git.gnome.org/browse/gsettings-desktop-schemas/log/?h=wip/window-scales
https://git.gnome.org/browse/gnome-settings-daemon/log/?h=wip/window-scales

Also, gnome-shell is pretty broken when Gtk+ is running in scaled mode,
so there is this badhack I use to make gnome-shell work with the above:
https://git.gnome.org/browse/gnome-shell/log/?h=wip/window-scales

Highres css assets require a branch atm:
https://git.gnome.org/browse/gnome-themes-standard/log/?h=wip/hidpi

Running with all the above on my Chromebook pixel things seems to mostly
work. There are some open issues:

* clutter doesn't respect the window scaling, so the gl rendering is too
  small.

* No support at all for using larger cursors or DnD icons

* As I said above, gnome-shell doesn't handle scaling at all

I'm leaving for vacation after friday and will be back for Guadec... I
might be around now and then, but not much.