Merge pull request #380 from ghalliday/issue378

FIX gh-378 Exit cache loop early (common case)

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>

system/jlib/jfile.cpp

@@ -6233,6 +6233,9 @@ public:
             if (!oldest)
                 break;
             oldest->cachedio.clear();
+            //If previously had max ios then we now have space.
+            if (n == max)
+                break;
         }
     }