Better reference for SHA-1

[Ben Harris <bjh21%bjh21.me.uk@localhost>]

It's getting a bit late, but I discovered yesterday that there's actually 
an RFC for SHA-1, so the references in [SSH-TRANS] to [FIPS-180-2] can be 
changed to refer to RFC 3174.

Aside: This has the interesting consequence that it gives us KEX 
(diffie-hellman-group14-sha1), host-key (ssh-rsa), MAC (hmac-sha1), and 
cipher (cast128-cbc) algorithms which are specified entirely by RFCs. 
It's a pity they're not all the required ones, really.  No, that's NOT a 
suggestion that the requirements be changed.

--
Ben Harris