Improve keyframe_insert performance for large amounts of keyframes

keyframe_insert run time appears to grow linearly with the amount of frames associated with an object. This becomes a disaster when one needs to import objects that contain several thousand frames of animation.

I have described the problem in-detail in this forum post .

Figures show a dependency of completion time of n=10000 runs of keyframe_insert on frame number:

1. Up to 5000 frames on a default cube
2. On the same default cube after creating 5000 keyframes with the first benchmark. This time the benchmark ran to

n=25000 frames