reverting r25862 (to working version of giac.js)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25864 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Tests improved for CAS

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25865 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e