Thanks to your feedback and pull requests we have a few bug fixes and an enhancement.
API:
Fix bug where std::weak_ptr was used in AbcCoreLayer instead of Alembic::Util::weak_ptr.
Add OCurves::Schema::Sample::setPositionWeights to go along with the get.
Expose it in the python bindings.
prman Procedural:
Add two options, -motionbegin and -motionend to explicitly control MotionBlocks.
(PR 160)