Fix for #3808: use ggbabs instead of abs

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@30314 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Improved variable ordering, to go with recent Giac changes

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@30315 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
[giac] updated tests

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@30316 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e