Vectiles constrain geom type

In some cases, postgis operations can cause the returned geometry type to be changed, e.g. a line can be clipped against a bounding box just on the very edge, turning it into a point. Clients typically expect the output geometry to be of the same type as the input, e.g. you want to be able to define a layer for rendering lines, and rely on getting back only lines. This is a small addition to the vector tile query to constrain geometries to the same type, but allows for MULTI geoms of the same underlying type to be mixed, e.g. a LINE is a valid output for a MULTILINE input, but a POINT is not.