Code cleaning in unification algorithm for universes.
Code cleaning in unification algorithm for universes.

This patch is only moving code around and expliciting statically the
invariants of the functions, so it should be 1:1 equivalent to the other
one. Amongst other goodies, the unification function is not recursive
anymore, which ensures that it will terminate.

SkySkimmer/coq,JasonGross/coq,Zimmi48/coq,gares/coq,amintimany/coq,coq/coq,JasonGross/coq,Lionel-Rieg/coq,letouzey/coq-wip,gares/coq,Lionel-Rieg/coq,letouzey/coq-wip,Zimmi48/coq,maximedenes/coq,SkySkimmer/coq,william-lawvere/coq,silene/coq,SkySkimmer/coq,amintimany/coq,Matafou/coq,silene/coq,Matafou/coq,gares/coq,maximedenes/coq,coq/coq,coq/coq,ppedrot/coq,JasonGross/coq,maximedenes/coq,ejgallego/coq,gares/coq,ejgallego/coq,william-lawvere/coq,Matafou/coq,maximedenes/coq,Zimmi48/coq,ppedrot/coq,ejgallego/coq,Lionel-Rieg/coq,coq/coq,ppedrot/coq,SkySkimmer/coq,silene/coq,maximedenes/coq,ejgallego/coq,letouzey/coq-wip,ppedrot/coq,gares/coq,JasonGross/coq,ppedrot/coq,letouzey/coq-wip,Zimmi48/coq,letouzey/coq-wip,amintimany/coq,william-lawvere/coq