[pretty-print py]Don't print sys.stdout;better utf
[pretty-print py]Don't print sys.stdout;better utf

This should fix #9705

I'm kind-of cargo-cult coding here, from things like
https://docs.python.org/3/library/sys.html#sys.displayhook and
https://github.com/coq/coq/issues/9705#issuecomment-471996313, but
hopefully this fixes the issue without breaking anything.  (I am really
a novice when it comes to the str/bytes distinction in python3.)

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