pool.Pool: store max_size as an attribute

eventlet/pool.py

@@ -6,6 +6,7 @@ class Pool(object):
     def __init__(self, min_size=0, max_size=4, track_events=False):
         if min_size > max_size:
             raise ValueError('min_size cannot be bigger than max_size')
+        self.max_size = max_size
         self.sem = coros.Semaphore(max_size)
         self.procs = proc.RunningProcSet()
         if track_events: