short_repr(): when processing tuple elements, use short_repr()

recursively to avoid blowing up when a tuple contains a really long
string (e.g. 100 MB in size).

src/ZEO/zrpc/log.py

@@ -57,7 +57,7 @@ def short_repr(obj):
         elts = []
         size = 0
         for elt in obj:
-            r = repr(elt)
+            r = short_repr(elt)
             elts.append(r)
             size += len(r)
             if size > REPR_LIMIT: