Warn if setuptools is incompatible with the build system

[manics]

Suggestion from https://forum.image.sc/t/release-of-omero-5-5-1/27545/4

Warn before running any build steps if the version of setuptools is incompatible with the build system.

[truatpasteurdotfr]

would it be possible also to avoid the pip commands as mentionned on https://docs.openmicroscopy.org/omero/5.5.1/sysadmins/unix/install-web/walkthrough/omeroweb-install-centos7-ice3.6.html:

pip install --upgrade pip
pip install --upgrade virtualenv

Or list the minimal version of virtualenv required?

[mtbc]

I'd expect any fairly recent virtualenv to work -- personally I often happen to use 15.1.0 instead of 16.7.0 -- so you could probably go ahead and try the installation without and test that things still work (including scripts, web apps, etc.), they probably will. However, do note that those installation walkthroughs are very close to what we actually test for releases so if you use older versions then do watch out for regressions when you upgrade OMERO and warn us (maybe with a pip freeze) if asking about issues for which the dependency versions may be relevant, especially as we sometimes try to reproduce users' installations in diagnosing their OMERO issues. The more you do differently from the installation walkthroughs, the further you are from a state that we are fairly sure should work fine. If there's some particular concern you have about using later dependency versions then please do feel free to raise it; in some circumstances we pin versions awhile to avoid specific issues.

[mtbc]

It's also worth noting that at the leading edge of OMERO development there is expected to be a fair bit of movement on Python 3 compatibility so that may have additional impact on module prerequisites over the coming months.