Fix higher-order pattern variables not being printed as "@?" (bug #5431).
Fix higher-order pattern variables not being printed as "@?" (bug #5431).

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