Separating this out because I was interested in comparing reverseDirectedEdge and directedEdgeToBoundary, since those are the two most expensive operations in my cellsToMultiPolygon implementation, so its useful to know how relatively expensive they are per edge.

On my laptop, I'm seeing that reverseDirectedEdge is usually about 12x faster:

./build/bin/benchmarkDirectedEdge
	-- directedEdgeToBoundary: 3.858900 microseconds per iteration (10000 iterations)
	-- reverseDirectedEdge: 0.305900 microseconds per iteration (10000 iterations)

coverage: 98.949% (+0.003%) from 98.946%
when pulling 0942c42 on ajfriend:aj/reverseDirectedEdge
into ddf8844 on uber:master.