X: set size hints before window is mapped
X: set base size hint
X: small cleanup
X: work around the mutter-3.14 bug

mutter-3.14 has a bug: it calculates aspect-based size constraints
for the entire window with decorators instead of for client area.
https://bugzilla.gnome.org/show_bug.cgi?id=739573

So for now we disable PAspect...