madt2709

Fix pow to work with negative tensors

3

[Fixes #1151](https://github.com/tinygrad/tinygrad/issues/1151).

When I call `sox.file_info.bitrate()` on a file I get the following error: ``` File "c:\Users\Theo\OneDrive\Documents\github\tinygrad\.venv\lib\site-packages\sox\file_info.py", line 64, in bitrate return float(output[:-1]) ValueError: could not convert string to float: '256k' ```...

Fix track_running_stats in batchnorm

2

-`test_batchnorm2d_no_running_stats` and `test_batchnorm3d_no_running_stats` catch the regression. Added two other tests for completeness.