fixed gae_memacache issue 1887, thanks mjwatson

VERSION

@@ -1 +1 @@
-Version 2.9.3-stable+timestamp.2014.03.03.08.49.54
+Version 2.9.3-stable+timestamp.2014.03.04.22.27.25

gluon/contrib/gae_memcache.py

@@ -17,15 +17,19 @@ class MemcacheClient(object):
 
     client = Client()
 
-    def __init__(self, request):
+    def __init__(self, request, default_time_expire = 300):
         self.request = request
+        self.default_time_expire = default_time_expire
 
     def __call__(
         self,
         key,
         f,
-        time_expire=300,
+        time_expire=None,
     ):
+        if time_expire is None:
+            time_expire = self.default_time_expire
+
         key = '%s/%s' % (self.request.application, key)
         value = None
         obj = self.client.get(key)