Update assetrtion of GetFeatureInfo.Mandatory

This Pull Request contains a fix for #5. Now,  the response entity is not expected to be an XML resource.

KVP.GetFeatureInfo.Mandatory was tested with [deegree webservices 3.4-pre15] (http://cite.lat-lon.de/deegree-webservices-3.4-pre15/). All other commits are not tested by me.