capi Voronoi Diagram Builder + tests

git-svn-id: http://svn.osgeo.org/geos/trunk@3953 5242fede-7e19-0410-aef8-94bd7d2200fb
Rename CAPI method GEOSVoronoiDiagramBuilder to GEOSVoronoiDiagram

See #627

git-svn-id: http://svn.osgeo.org/geos/trunk@3954 5242fede-7e19-0410-aef8-94bd7d2200fb