moved graph traversal functionality up to Hashtable base class from Hashbits
removed unused/mostly untested traversal and graph complexity code
initial code for graph partitioning based on abundance
fixed bug in count_partitions; fixed associated tests; abundance partitioning works
Merge branch 'master' of github.com:ged-lab/khmer into graph_partitioning_on_abundance

Conflicts:
	lib/hashbits.hh
added some comments to abundance partitioning tests
added compare_partitions function
added another test for partition comparison
added subset_partition_size_distribution function to counting hashes
added code for SubsetPartition objects in Python
shifted counting hash subset functions onto the new subset object
added partition_sizes function to retrieve partition IDs & sizes
added partition_sizes test
replaced now-missing function hash_subset_count_partitions for hashbits
added partition coverage calculations
added some simple tests for partition average coverages
Merge branch 'master' of github.com:ctb/khmer into graph_partitioning_on_abundance
Merge remote-tracking branch 'ged/master' into graph_partitioning_on_abundance

Conflicts:
	lib/Makefile
prototype script for running abundance partitioning
Merge branch 'graph_partitioning_on_abundance' of github.com:ged-lab/khmer into graph_partitioning_on_abundance