tests/testlib/common.sh

mail: force SMTPException to bytes before wrapping in error.Abort

Pytype wasn't complaining about this for some reason, but PyCharm was and we
already handle another instance of this exception the same way in this function.

Differential Revision: https://phab.mercurial-scm.org/D10473

mkcommit() {
   name="$1"
   shift
   echo "$name" > "$name"
   hg add "$name"
   hg ci -m "$name" "$@"
}