Better error message for nested module application.
Better error message for nested module application.

Fixes #3809.

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