Clarify the Ltac2 invalid identifier message.
Clarify the Ltac2 invalid identifier message.

silene/coq,coq/coq,silene/coq,gares/coq,coq/coq,ejgallego/coq,Zimmi48/coq,JasonGross/coq,Zimmi48/coq,coq/coq,silene/coq,ejgallego/coq,ejgallego/coq,gares/coq,SkySkimmer/coq,JasonGross/coq,JasonGross/coq,gares/coq,SkySkimmer/coq,SkySkimmer/coq,Zimmi48/coq,gares/coq,ejgallego/coq,JasonGross/coq,Zimmi48/coq,SkySkimmer/coq,coq/coq,gares/coq