Represents a WMS GetMap request. as a extension to the WMS spec 1.1.
author: Gabriel Roldan, Axios Engineering author: Simone Giannecchini version: $Id: GetMapRequest.java 7639 2007-10-22 15:18:58Z aaime $
DJB: spec says SRS is *required*, so if they dont specify one, we should throw an error
instead we use "NONE" - which is no-projection.
Previous behavior was to the WSG84 lat/long (4326)
request CRS, or null if not set.TODO: make CRS manditory as for spec conformance