Renamed start to frame_start and end to frame_end for generating particles, so that the cloud gen script works again.

collections like context.selected_objects no longer return None for empty lists. Update scripts for this.
also removed check for obj.data == None for a mesh. This will never happen.

add contrib\py\scripts\addons\space_view3d_multiselect_menu.py
delete contrib\py\scripts\addons\space_view3d_cursor_menu.py
too many conflicts if enabled with dynamic menu & is integrated into Dynamic menu & spacebar menu

[[Split portion of a mixed commit.]]

moved directly to trunk/py/scripts/addons/object_cloud_gen.py