[giac] Update to giac 1.1.0-20:
- fix for groebner basis
- fix for multivariate polynomial factorization
- fix for regroup (hope it will not break anything in ggb).
- changed caseval to run evaluation in a separate thread. However I don't know how to cancel it cleanly without std exceptions enabled. 
- other CAS fixes should not interact with ggb (?)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@29627 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e