Stuff for 2.4.1

I've integrated a few patches in my repos. The most import is own
parser for the bytea hex format, so that clients are no more dependant
on libpq 9 to talk with a 9 server. By the way the best way to make
this patch was to have our own parser for the "escape" format as well:
this has generally improved performance in receiving bytea
(PQunescapeBytea required a null-terminated string even if we know the
length of the string to decode, so we dropped unneeded memcpy/strlen
of the received data).

Other things are minor, see the news file
(https://github.com/dvarrazzo/psycopg/blob/devel/NEWS).

If I haven't forgotten anything I think we can have a 2.4.1 release.

Cheers,

-- Daniele