[Distutils] patch: ez_setup.py: separate default version and minimum version of setuptools

[zooko]

>> Thank you for setuptools!  We are using it in the Allmydata-Tahoe
>> project [1].  We've patched ez_setup.py so that installation can
>> proceed if an older version of setuptools is already present, as long
>> as that version is not too old.  This allows ez_setup.py to work
>> seamlessly in more situations.  Please apply.

> It's not clear to me why the patch is necessary.  If you reference  
> a specific version of setuptools in your call to ez_setup(), the  
> behavior is almost identical.  The only difference is that if there  
> is no setuptools installed, then the version you specified in your  
> setup.py will be used for the installation.

The situation was that a user had a version of setuptools installed  
(I think it was v0.6c5), and the ez_setup.py specified setuptools  
v0.6c6 (which was at that time the current version).  So, when the  
user executed "./setup.py", then he got an error saying that it  
wasn't possible to upgrade setuptools after setuptools was already  
loaded.

With our patch, this is no longer a problem -- v0.6c5 is new enough  
to work, and so the setup.py execution proceeds after the check  
without attempting to install a newer version of setuptools.

Regards,

Zooko