BUG: setup.py error message lacks cache_dir argument

Author: y-p

setup.py

@@ -341,7 +341,7 @@ def __init__(self,*args,**kwds):
         cache_dir=kwds.pop("cache_dir",BUILD_CACHE_DIR)
         self.cache_dir=cache_dir
         if not os.path.isdir(cache_dir):
-            raise Exception("Error: path to Cache directory [%s] is not a dir");
+            raise Exception("Error: path to Cache directory (%s) is not a dir" % cache_dir);
 
     def _copy_from_cache(self,hash,target):
         src=os.path.join(self.cache_dir,hash)