- add a limit evaluation method to EvalLimitController that allows
client code to directly pass the output buffer without binding it
to the Context (the call only computes vertex interpolation of a
single sample)
- switch the OsdUtilAdaptiveEvaluator to use the new method from the controller
and stop stomping member
- cleanup buffer and member variables no longer used
- cleanup initialization logic to be better aware of uniform / adaptive
- add some assert sanity checks in the cpuEvalLimitKernels
fixes#293
