In addition create a similar method that doesn't copy objects.
Benchmark for the new no-copy method vs the old one:
```
benchmark old ns/op new ns/op delta
BenchmarkGetControllerOf-12 214 14.8 -93.08%
benchmark old allocs new allocs delta
BenchmarkGetControllerOf-12 1 0 -100.00%
benchmark old bytes new bytes delta
BenchmarkGetControllerOf-12 80 0 -100.00%
```
Benchamrk for the new (copy) method vs the old one:
```
benchmark old ns/op new ns/op delta
BenchmarkGetControllerOf-12 128 114 -10.94%
benchmark old allocs new allocs delta
BenchmarkGetControllerOf-12 1 1 +0.00%
benchmark old bytes new bytes delta
BenchmarkGetControllerOf-12 80 80 +0.00%
```
Overall there is a 10% improvement for the old vs new (copy) method and
huge improvent (x10) for the old vs new (no-copy).
I changed the IsControlledBy and a few other methods to use the new (no-copy) method.
01ccd2e19e