[giac] various fixes, improves integration of 1/surd and diff(y(x),x,n)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25286 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@25287 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e