Fix RobustLineIntersector handling of invalid intersection points (#622)

Adds new testcases. Many of them fail, probably due to the lack of
double double use, but one of them only fails with the old
RobustLineIntersector heuristic handling invalid intersection points

git-svn-id: http://svn.osgeo.org/geos/branches/3.3@3788 5242fede-7e19-0410-aef8-94bd7d2200fb