[giac] fix Expand[ ]

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@24856 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
[giac] updated unit tests

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@24857 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e