this is kind of a "suggested change" for the API controller to

this is kind of a "suggested change" for the API controller to
support an additional "restriction" parameter for the "map"
call (only value currently supported: nodes_only to return only
nodes). i would have liked to implement "tagged_nodes_only" as
well but was unsure how to do that best. feel free to make up
some other way instead to improve node access for POI editors,
or drop this altogether if you have some other grand plan.