melting-pot: warn less about unpinned deps

In particular: only warn if it's an unpinned dependency from the most
recent success (i.e. first row of the cached successes), rather than
warning about every single unpinned dependency present in every single
cached past success, no matter how old.

Author: ctrueden

melting-pot.sh

@@ -669,7 +669,8 @@ do
         mismatch="$mismatch\n* $g:$a:$v -> $bomV"
       else
         # G:A version is not pinned.
-        warn "$1: Unpinned dependency: $dep"
+        test "$row" -ne 1 ||
+          warn "$1: Unpinned dependency: $dep"
       fi
     fi
   done