[giac] adding rootof() to parser (unhandled)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25299 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
[giac] workaround for complex division by 0 not working in js, also avoids rootof in output in ggb mode

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25300 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e