Add OS X support.
Merge branch 'master' of git://github.com/habnabit/libcurvecpr into add-os-x-support
Updated OS X support code.

* Fixed warnings in existing implementation.
* Cached port returned by host_get_clock_service().
* Added unit test for curvecpr_util_nanoseconds().

Refs #4.
Merge branch 'add-os-x-support'

Closes #4.