Univ: correct compare_neq (fix #2703)
Univ: correct compare_neq (fix #2703)

 The earlier version was a bit too quick to answer <= while strict
 constraints could still appear from remaining universes to explore.
 Typical situation: compare u v when u <= v and u <= w < v.
 Encountering u <= v isn't enough to conclude yet...

 This means that kernels from r13719 to now in trunk, and
 from r13735 to now in 8.3 (including 8.3pl{1,2,3}) couldn't accurately
 detect universe inconsistencies, leading to potential proofs of False!
 Oups, sorry...

git-svn-id: 44dc50bdcc0f5d1a212c497508dc9452e0b35e2b@14993 85f007b7-540e-0410-9357-904b9bb8a0f7

letouzey/coq-wip,barras/coq,SkySkimmer/coq,SkySkimmer/coq,TOSPIO/coq,maximedenes/coq,Lionel-Rieg/coq,8l/coq,herbelin/github-coq,maximedenes/coq,herbelin/github-coq,shindere/coq,amintimany/coq,aspiwack/coq,william-lawvere/coq,Ptival/coq,gmalecha/coq,coq/coq,pirapira/coq2rust,gares/coq,william-lawvere/coq,silene/coq,Matafou/coq,ppedrot/coq,letouzey/coq-wip,Lionel-Rieg/coq,JasonGross/coq,maximedenes/coq,letouzey/coq-wip,shindere/coq,Ptival/coq,aspiwack/coq,silene/coq,pirbo/coq,mattam82/coq,TOSPIO/coq,8l/coq,barras/coq,Zimmi48/coq,ppedrot/coq,TheTypoMaster/coq,shindere/coq,pirapira/coq2rust,maximedenes/coq,silene/coq,william-lawvere/coq,asr/coq,ejgallego/coq,ale-f/coq,letouzey/coq-wip,coq/coq,TheTypoMaster/coq,maximedenes/coq,JasonGross/coq,mattam82/coq,mlasson/coq,jpdeplaix/coq,jpdeplaix/coq,TheTypoMaster/coq,ejgallego/coq,gares/coq,gmalecha/coq,ejgallego/coq,herbelin/github-coq,SkySkimmer/coq,8l/coq,Matafou/coq,Ptival/coq,pirbo/coq,asr/coq,coq/coq,Matafou/coq,Zimmi48/coq,Zimmi48/coq,gmalecha/coq,coq/coq,asr/coq,pirbo/coq,ppedrot/coq,JasonGross/coq,jhjourdan/coq,amintimany/coq,gares/coq,mlasson/coq,ale-f/coq,jhjourdan/coq,SkySkimmer/coq,gares/coq,ppedrot/coq,ppedrot/coq,ejgallego/coq,JasonGross/coq,jpdeplaix/coq,pirapira/coq2rust,Zimmi48/coq,Lionel-Rieg/coq,barras/coq,aspiwack/coq,TOSPIO/coq,jhjourdan/coq,gares/coq,mlasson/coq,amintimany/coq,letouzey/coq-wip,ale-f/coq,mattam82/coq