added impose_hyps_tac; robustify insts of tactic emulations;
added impose_hyps_tac;
robustify insts of tactic emulations;

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