Try to preserve more sharing in nf_evars_and_universes_opt_subst.
Try to preserve more sharing in nf_evars_and_universes_opt_subst.

SkySkimmer/coq,SkySkimmer/coq,ejgallego/coq,ejgallego/coq,Zimmi48/coq,gares/coq,ejgallego/coq,JasonGross/coq,gares/coq,JasonGross/coq,coq/coq,SkySkimmer/coq,Zimmi48/coq,coq/coq,SkySkimmer/coq,silene/coq,Zimmi48/coq,silene/coq,Zimmi48/coq,gares/coq,silene/coq,coq/coq,gares/coq,JasonGross/coq,ejgallego/coq,coq/coq,JasonGross/coq,gares/coq