- Updated createflowpaths 10a1 to ensure that the generation of a single
  flow table results in an equivalent flow table as CF9.1
- Fixed bug introduced in build_flow_table where flow_table[pch].num_adjacent
  was reset to zero, resulting in the adjacency list of a patch to be reset
  by check_neighbours in subsequent iterations of build_flow_table.
Fixed makefile which was failing under OS X: added missing initialization of OS
variable
Implementation of hash table data structure to be used for speeding up
find_patch
Initial application of patch hash table to replace find_patch.  Next update
will refactor this to make find patch use the hash table
Added missing include from previous commit
- Refactored find_patch to use patch hash table instead of doing a full
  flow table scan for each call
- Finished implementation of hash table speed up to find_patch
- Finished reworking sort_flow_table to use stdlib's merge sort instead of
  bubble sort