vsc/__init__.py file missing when doing "pip install" with "--prefix=xx" about vsc-install HOT 4 OPEN

In case it's useful, I saw this today when installing without admin rights on a CentOS 6 system, which I was using a Python 2.7.11 module, to get around a known problem with SSL libraries when using the native Python.

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Since pip is claiming there isn't anything they can do about this we'll probably have to look at working around that limitation in pip. But I'm not sure how we can detect we're being used by (a broken) pip and not a working setuptools.

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I think the proper fix here is to switch to using pkgutil.extend_path rather than pkg_resources.declare_namespace, which works fine with pip, see also https://packaging.python.org/guides/packaging-namespace-packages/#creating-a-namespace-package .

We made that change in EasyBuild recently (see easybuilders/easybuild-framework#2836) didn't encounter any real problems since we did.

The (big) downside is that once we start using pkgutil.extend_path somewhere, we have to start using it in all other vsc-* packages on short notice, since it doesn't mix well with pkg_resources.declare_namespace

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We used to have declare namespace but this didn't work for zipped eggs (iirc), see discussion in
#21

and pr where we switched from declare namespace to extend_path: #6

it also failed for some other reasons
and my answer to my own question here:
https://stackoverflow.com/questions/12040689/add-a-subdirectory-to-a-python-namespace/12041007#12041007

but if you got it working in EB, you might have found the correct workarounds?

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