Opens a new display, sets it up, initialises all the X extensions we will need, and adds it to the list of displays.
This is a list of the names of all the X atoms that Metacity uses. Each is wrapped in a macro "item()" which is undefined here; the idea is that when you need to make a big list of all the X atoms, you can define item(), include this file, and then undefine it again.
If you also define EWMH_ATOMS_ONLY then you will only get _NET_WM_* hints rather than all of them.
Definition in file atomnames.h.