[Distutils] Simultaneous multi-version support

[zooko]

We use pkg_resources.require() in Tahoe solely in order to get better  
and earlier error messages in the case of missing or wrong-version  
dependencies:

http://allmydata.org/trac/tahoe/browser/_auto_deps.py?rev=2968#L22

"""
The purpose of this function is to raise a pkg_resources exception if  
any of the
requirements can't be imported.  This is just to give earlier and  
more explicit error
messages, as opposed to waiting until the source code tries to import  
some module from one
of these packages and gets an ImportError.  This function gets called  
from
src/allmydata/__init__.py .
"""

We are considering experimenting with the multi-version feature of  
eggs, but haven't tried it yet.

pkg_resources.require() is not particularly problematic for us as far  
as I recall.

Regards,

Zooko
---
http://allmydata.org -- Tahoe, the Least-Authority Filesystem
http://allmydata.com -- back up all your files for $5/month