[Patch] Keyboard accelerators for actions

[Holger Berndt <berndth gmx de>]

Attached are two small patches for enhancing keyboard shortcut support
of Nautilus. The first patch enables the user to assign keyboard
shortcuts to scripts (provided that can-change-accels is true). The
second patch provides save/restore functionality to preserve the
shortcuts accross restarts.

Regards,
Holger