[giac] improvements related to #3509. Also small speedup for Groebner basis. A few bug fixes.

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@27881 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Changing giac.js to the latest version in web/kickstart.xml

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@27882 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e