Don't read most properties for override-redirect windows

Skipping handling of properties for override redirect windows has
two advantages: first it reduces the amount of work needed to get
an override-redirect window (menu, tooltip, drag icon) onto the
screen. But more importantly, it reduces the number of code-paths
for an override-redirect to get into some code portion where it
isn't expected.

* Integrate the list of properties we load initially with the
  list of property hooks; this avoids having two separate lists
  that we have to keep in sync.

* Add a flag to MetaWindowPropHooks to indicate whether the
  property should be handled for override-redirect windows;
  currently we load a) properties that identify the window -
  useful for debugging purposes b) WM_TRANSIENT_FOR (could be
  used to associate menus with toplevels.)

* For properties that aren't always loaded through window-props.c,
  add !window->override checks to places that trigger loading,
  and add g_return_if_fail(!window->override) to the load
  functions as a double-check.

http://bugzilla.gnome.org/show_bug.cgi?id=582639