[crypto] Encode unicode strings in _cypherer() pycrypto accept both bytes or string but pycryptodome, which will be introduced in next changeset, doesn't accept this. For backward compatibility, encode unicode strings in _cypherer()

version=3
opts=uversionmangle=s/(rc|a|b|c)/~$1/ \
https://pypi.debian.net/cubicweb/cubicweb-(.+)\.(?:zip|tgz|tbz|txz|(?:tar\.(?:gz|bz2|xz)))