Changing the separator for appended string options to comma.
Changing the separator for appended string options to comma.

This is a bit ad-hoc, but looks better for warnings since there is
a command-line flag accepting the same values, so comma will lead to
fewer parsing issues than space.

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