Using myeliminate for the locus equation computation as well (Giac speedup), may be backported to 4.4

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@29872 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Forgotten from previous commit

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@29874 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e