Get snapping to character grid working again, avoid crashes when attempting
to resize below 1x1 character cell, only redraw when size actually changes.
Also, rename window_get_child_rectangle() to window_get_child_allocation().
The new map_toplevel() request no longer specifies a position and takes
the size from the attached buffer. The attach request now takes a
position relative to the top-left corner of the old buffer to let
clients specify the relative position of the new buffer.
This is an example of how to animate window resizing. The size is
animated by a simple physics model that allows the user to cancel the
animation halfway and still look good.
