[giac] desolve now handles linear differential system with cst coeffs, e.g.
desolve([y'=[[1,2],[2,1]]*y+[x,x+1],y(0)=[1,2]]);
Fix for odesolve in reverse time direction
Other changes should not affect ggb.

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@30857 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e