new mmdet dependency does not support windows

[fcakyon]

The official pycocotools does not provide windows support because of this line in setup.py, how to use mmdetection on windows after this pr?

[hhaAndroid]

If mmpycocotools can be installed successfully, I think pycocotools can also be used, because mmpycocotools simply wraps pycocotools.

[fcakyon]

@hhaAndroid it is not true. Please compare this line in pycocotools and mmpycocotools.

mmpycocotools fixes windows installation bug of original pycocotools by commenting out that line in setup.py.

[fcakyon]

With this commit, @xvjiarui added windows installation support to mmpycocotools, before that it was not possible to install mmdet on windows.

[hhaAndroid]

With this commit, @xvjiarui added windows installation support to mmpycocotools, before that it was not possible to install mmdet on windows.

OK, Thank you. I will confirm it.