Fixing Giac errors due to wrong mode setting

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@28438 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Using closeString

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@28439 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e