WMS - undefined behavior with top-level layer from capabilities

[dmorissette]

The capabilities document always includes a top-level layer but nothing is done 
to handle the case where one selects that layer via the LAYERS parameter of a 
getMap request.

TODO: Make it so that if one selects the top-level layer in the LAYERS
parameter of a getMap request then all the layers in the map are turned
on.

[dmorissette]

Fixed.  If top-level layer is requested then all layers are turned on.