Fix WfsCapabilities reader for WFS 1.1.0.

See https://github.com/geoext/geoext2/issues/281. This is a port of the
approach taken in GeoExt 1: https://github.com/geoext/geoext/pull/30.
Merge pull request #282 from marcjansen/wfs110-capability

Fix WfsCapabilities reader for WFS 1.1.0.