* src/glade-command.c: glade_command_cut_copy_paste_common(); fixed
	  "project" source in case of `type == GLADE_PASTE'

	* src/glade-editor-property.c: Clean up compiler warnings, removed useless
	  mnemonic label.

	* src/glade-project.[ch], src/glade-property.c, src/glade-widget.[ch]:
	  Implemented references on widgets from object properties, object properties
	  are automaticly set to NULL when the target object is removed from its
	  project, an undo will result in the object being re-added to the project;
	  and its reffered properties to be reset to thier previous value.