drc will flag parts that self-overlap

git-svn-id: http://fritzing.googlecode.com/svn/trunk@6990 85f94c43-f63a-0410-9d22-21439860c375
slightly better overlap detection

git-svn-id: http://fritzing.googlecode.com/svn/trunk@6991 85f94c43-f63a-0410-9d22-21439860c375