Stop using unqualified {GET,PUT}_32BIT.

Those were a reasonable abbreviation when the code almost never had to
deal with little-endian numbers, but they've crept into enough places
now (e.g. the ECC formatting) that I think I'd now prefer that every
use of the integer read/write macros was clearly marked with its
endianness.

So all uses of GET_??BIT and PUT_??BIT are now qualified. The special
versions in x11fwd.c, which used variable endianness because so does
the X11 protocol, are suffixed _X11 to make that clear, and where that
pushed line lengths over 80 characters I've taken the opportunity to
name a local variable to remind me of what that extra parameter
actually does.

agentf.c

@@ -72,7 +72,7 @@ static void agentf_try_forward(agentf *af)
             break;         /* not even a length field available yet */
 
         bufchain_fetch(&af->inbuffer, msglen, 4);
-        length = GET_32BIT(msglen);
+        length = GET_32BIT_MSB_FIRST(msglen);
 
         if (length > AGENT_MAX_MSGLEN-4) {
             /*