Fix format string mistakes revealed by new checking.

An assortment of errors: int vs size_t confusion (probably undetected
since the big switchover in commit 0cda34c6f), some outright spurious
parameters after the format string (copy-paste errors), a particularly
silly one in pscp.c (a comma between two halves of what should have
been a single string literal), and a _missing_ format string in ssh.c
(but luckily in a context where the only text that would be wrongly
treated as a format string was error messages generated elsewhere in
PuTTY).

sshshare.c

@@ -1794,8 +1794,9 @@ static void share_receive(Plug *plug, int urgent, const char *data, size_t len)
     }
     if (cs->recvlen > 0 && cs->recvbuf[cs->recvlen-1] == '\015')
         cs->recvlen--;                 /* trim off \r before \n */
+    ptrlen verstring = make_ptrlen(cs->recvbuf, cs->recvlen);
     log_downstream(cs, "Downstream version string: %.*s",
-                   cs->recvlen, cs->recvbuf);
+                   PTRLEN_PRINTF(verstring));
     cs->got_verstring = true;
 
     /*