Add accumulator-based tiling.  Make sure it works interchangably with RDDBinner-based tiling (but leave non-on-demand tests using RDDBinner-based tiling, so as to exercise RDDBinner too).  Use accumulator-based tiling in on-demand demo and tile service in general
Merge pull request #51 from oculusinfo/accumulator-tiling

Add accumulator-based tiling.