Can't use opencv-python due to --no-binary

Our requirement file has, among other packages:
```
opencv-python==3.3.0.9
```
However, pip-requirements-file and pip-install-simple use the `--no-binary :all:` option when calling `pip`.

Is there any option to download the packages anyway?

I saw this was introduced in v0.2.0, I'm trying version v0.1.3 now.

Start by tracing the requirement-file and install entry points named pip-requirements-file and pip-install-simple, including where pip is invoked with --no-binary :all:. Compare the behavior introduced in v0.2.0 with v0.1.3 and determine what change would allow opencv-python==3.3.0.9 to be downloaded; done means the package can be handled through the requirement file.

Written by the indexing model from the issue text.