constraints: don't apply fullscreen workarounds for CSD windows

If you maximize a CSD window on a monitor without struts, it ends up
taking the whole monitor size, but it doesn't mean that the application
wants to fullscreen.

Gnome Bug:
https://bugzilla.gnome.org/show_bug.cgi?id=708718
Gnome Commit:
https://git.gnome.org/browse/mutter/commit/src/core/constraints.c?id=4eeeb1557a3a0caff6ef1debd92aeb541ae1b556
Merge pull request #80 from infirit/1.6

constraints: don't apply fullscreen workarounds for CSD windows