Slight modification of test.

We don't want the two ends of the path to be within the same node. This
triggers the exception.
First level of parallelism works.
Splitting processing four ways works, but performance terrible.

We need to rethink the split strategy. Set for single thread until Greg
has more time to revisit parallelization.
Merge branch 'issue5' into develop
Updated issues.mkd regarding issue5

This will have to be re-investigated at a later date. The parallel
Dijkstra's algorithm works, but performance degrades as threads are
added, probably due to the parallelization.