fix problem with setting Vector's startpoint (#4160)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@33889 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
revert the rest of r33744 (#4160)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@33890 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
[giac] fix for #4325

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@33891 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e