Render LinearRings in WPS WKT output as LineStrings

The JTS library defines a LinearRing geometry type; however, this
geometry type is not defined in WKT.  As noted in the API documentation
for JTS' WKTWRiter:

> A non-standard LINEARRING tag is used for LinearRings. The SFS WKT spec
> does not define a special tag for LinearRings. Under it, rings are
> output using LINESTRING.

In my use case OpenLayers does not account for this nonstandard encoding
and I believe the best fix is for GeoServer to ensure standard compliant
output.
Merge pull request #753 from dwins/wps-wkt-linearrings

Render LinearRings in WPS WKT output as LineStrings
[GEOS-6697] Avoid adding null messages in exception reports
Merge branch 'master' of git://github.com/geoserver/geoserver