switch cpuEvalLimitController to use a quad-tree based patch access map :

- remove PatchMap from FarPatchTables

- add a new FarPatchMap quad-tree class (constructed from FarPatchTables)

- refactor the EvalLimitController to use the quad-tree search instead of a
  serial loop access

fixes #174
Merge branch 'dev' of github.com:PixarAnimationStudios/OpenSubdiv into dev