  This paper has been withdrawn by the authors because the ratio presented in
Eq. (13) does not remain frozen in time for all values of w = p/rho. As such a
separate more detailed analysis containing the generalized Buchdahl inequality
valid for all values of w is required. The new analysis will in addition attend
to the time evolution of the ratio (13). The essential results remain
unchanged, but result from the w=0 case.
