Added singleton_iff, Sigma_empty1, Sigma_empty2, Collect_simps and UnInt_simps to ZF_ss.  Added consI1 to ZF_typechecks.
Added singleton_iff, Sigma_empty1, Sigma_empty2, Collect_simps
and UnInt_simps to ZF_ss.  Added consI1 to ZF_typechecks.

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle