debug prints; filter fixes; potential issue with spurious flow remove counts uncovered:

To see the spurious extra counts in flow removes, first run tshark/wireshark
on the side to only capture IP and ARP packets in the mininet network. Then start the
controller with bucket.py, and do

h1 ping -c 2 h2

in mininet. You should see multiple flow removed messages printed in the output of the
controller. These packet and byte counts clearly outnumber the number of packets actually
on the network as seen from wireshark/tshark.

Notes:
1. For info on filters to use for wireshark/tshark to see this, check the debugging section
   on the pyretic-dev wiki:
   https://github.com/frenetic-lang/pyretic-dev/wiki

2. OVS may potentially be the cause of this problem. See
   http://openvswitch.org/pipermail/discuss/2011-May/005181.html
   for similar bugs being reported. In general OVS counts in flow removed messages are
   "best effort".
updated filters for bucket.py tests
fix bug where bucket dictionary changes while in loop
revert error prints to debug prints