improve deprecation message for minus_plus
improve deprecation message for minus_plus

SkySkimmer/coq,SkySkimmer/coq,SkySkimmer/coq,SkySkimmer/coq,coq/coq,ejgallego/coq,ejgallego/coq,Zimmi48/coq,ejgallego/coq,ejgallego/coq,coq/coq,Zimmi48/coq,coq/coq,coq/coq,Zimmi48/coq,Zimmi48/coq