Since we're not setting the frame's output shape any more, it doesn't
make sense to calculate the output shape based on the frame window.
Instead, track the client window directly and calculate the output shape
based on that.
https://bugzilla.gnome.org/show_bug.cgi?id=644930
If mutter is going to be a "real" library, then it should install its
includes so that users can do
#include <meta/display.h>
rather than
#include <display.h>
So rename the includedir accordingly, move src/include to src/meta,
and fix up all internal references.
There were a handful of header files in src/include that were not
installed; this appears to have been part of a plan to keep core/,
ui/, and compositor/ from looking at each others' private includes,
but that wasn't really working anyway. So move all non-installed
headers back into core/ or ui/.
https://bugzilla.gnome.org/show_bug.cgi?id=643959
