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.

sftp.c

@@ -38,7 +38,7 @@ struct sftp_packet *sftp_recv(void)
     if (!sftp_recvdata(x, 4))
 	return NULL;
 
-    pkt = sftp_recv_prepare(GET_32BIT(x));
+    pkt = sftp_recv_prepare(GET_32BIT_MSB_FIRST(x));
 
     if (!sftp_recvdata(pkt->data, pkt->length)) {
 	sftp_pkt_free(pkt);