So far nothing prevented a client for registering a surface as one type
and then as another type. With some special types, this would lead to
corrupted wl_lists.
Add a function, that either resets the surface type or posts an error to
the client. In case of an error, the set type operation must be aborted.
Change the type name SHELL_SURFACE_NORMAL to SHELL_SURFACE_NONE, as
there is nothing normal in the "none" type which just means uninitialised.
Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
9826223a1b