pycompat: alias urlreq.unquote to unquote_to_bytes...
pycompat: alias urlreq.unquote to unquote_to_bytes
Previously, urlreq.unquote aliased to urllib.parse.unquote,
which returned a str/unicode. We like bytes, so switch urlreq.unquote
to dispatch to urllib.parse.unquote_to_bytes.
This required a minor helper function to register an alias under a
different name from which it points. If this turns into a common
pattern, we could likely teach _registeralias to accept tuple
values defining the mapping. Until then, I didn't feel like
adding complexity to _registeralias.
