fix MAX_QUEUE_SIZE to match config file default

It's not really clear what to do here. If someone has altered their
config file to remove this line, this patch will alter behaviour of
their instance. However, the example config default has been 10000 since
first commit, and that's probably a more sensible default value. It
might nonetheless be more sensible to just document the discrepancy.

lib/carbon/conf.py

@@ -68,7 +68,7 @@
   MAX_DATAPOINTS_PER_MESSAGE=500,
   MAX_AGGREGATION_INTERVALS=5,
   FORWARD_ALL=True,
-  MAX_QUEUE_SIZE=1000,
+  MAX_QUEUE_SIZE=10000,
   QUEUE_LOW_WATERMARK_PCT=0.8,
   TIME_TO_DEFER_SENDING=0.0001,
   ENABLE_AMQP=False,