If external CAS present, do not initialize (ends in inf. loop)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@32895 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Update IsPrime when getting defined

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@32896 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e