Pulling back some updates to BRISK that were done for Google Tango.
move local opencv wrapping implementation to namespace to avoid conflict with opencv when opencv is preloaded by another lib. (Tango only)
Some more wrappers to access keypoint members from both opencv and cvFlyby, these are verified to get inlined and optimized so that there is no perf. penalty
Pulling back some updates to BRISK that were done for Google Tango.