GML: support reading WFS 2.0 GetFeature documents with wfs:FeatureCollection as a wfs:member of the top wfs:FeatureCollection

git-svn-id: https://svn.osgeo.org/gdal/trunk@26643 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_travis_macosx