partial complete PCount refractor to measure loss for ALL flows between switches

ultimately, this change will be removed and reverted back to the per-flow approach of packet loss measurement
refactored PCount to work with Merger algorithm
added support for computing number of flows to garbage collect

only computes the statistics, does not actually remove the stale flows
cleaned up deprecated code
cleaned up deprecated code
fixed issue with PROACTIVE and Baseline, now write the tree_id at the root node

writes the backup tree_id at the root node, and matches using this id at any nodes in both primary and backup tree but have different outports across the two trees
new figures for another multicast-test.py test case
completed implementation to preinstall flow rules that match using Bid when necessary + computing activation flows at multicast tree root node

as a result i had to make changes to the Reactive Backup Tree Activation Mode.  included new unit tests with better coverage of implementation.
added PCount implementation that monitors all flows traversing (u,d)

this code is in pcount_all.py.  the other files (appleseed and multicast.py) are updated to use pcount_all.py
PCount experiment works for a single number of monitored flows but iterating over all window sizes
this is actually the complete version of the PCount experiments for a fixed number of monitored flows
PCount expt works for all W and iterates through all number of flows
PCount Experiments for (1) loss rate vs w and (2) processing time vs number of flows work

for (2) still need to create the extra flows at the switches to examine overhead of table size
revised PCount Expt code and support files
commit before merging Nick's changes.  pcount_all.py experiments are setup and run correctly
update to .gitigore
update to .gitignore
Merge remote-tracking branch 'origin/debugger' into debugger

Conflicts:
	.gitignore
	ext/multicast.py
merged nick's stainer arboresence changes.  made modifications to multicast and multicast_test to ensure all tests pass

also had to comment out some unused package imports in SteinerArboresence to allow the code to run