sticky points for move plane: avoid plane jumping

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@37848 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Ticket #3420: at least doing something that works, until better implementation (but it seems nothing works in IE)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@37849 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e