Temporary revert commit 14550 since it breaks a few contribs
Temporary revert commit 14550 since it breaks a few contribs

 Interestingly, it appears that the Not_found in heads.ml is actually
 triggered in some contribs, but catched. Maybe a "try" tactical ?
 Are these Not_found another effects of bug #2608 or something similar ?
 Anyway, replacing Not_found by "assert false" currently breaks these
 contribs. So for the moment, we revert to the original code. When bug
 #2608 will have been solved, we'll try again enabling these "assert false".

git-svn-id: 44dc50bdcc0f5d1a212c497508dc9452e0b35e2b@14560 85f007b7-540e-0410-9357-904b9bb8a0f7

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