macosx: use an updated API to set the behavior of menu bar and Dock in fullscreen mode on 10.6&later

this allows the user to access the Dock while in fullscreen mode in contrast to the previous implementation. behavior on 10.5 did not change.

Modules are created at initialization and destroyed at exit (after all
VLC threads are terminated) There is no need to count references.

This property is fundamentally per-plugin, not per-submodule.

This field is never used for submodules, and in fact there would be no
way to show it in the (current) UI.

This is the same as module_t.pp_shortcuts[0].

Use NULL rather than a static string as the default.
module_get_object() deals with this situation.

The module will never be proved. This applies to the "main" module
and the playlist demux (which only has submodules).