[Distutils] Automatically going for a pre-req dev

[Ben Bangert]

When installing a package that requires the dev version of another  
package, it fails to to and download a dev version of the package.  
This appears to be because it either searches the filesystem for the  
prereq version, or asks CheeseShop.

Given that the prereq indicates it wants a dev version, it would seem  
reasonable to search CheeseShop with ==dev equivalent active.

As an example, if you install:
easy_install -U hellahella==dev

It installs fine from svn, then goes back searching for Pylons, and  
gets:
Processing dependencies for hellahella==0.1dev-r576
Searching for Pylons>=0.1dev-r289
Reading http://www.python.org/pypi/Pylons/
Reading http://pylons.groovie.org/
No local packages or download links found for Pylons>=0.1dev-r289
error: Could not find distribution for Requirement.parse 
('Pylons>=0.1dev-r289')

Yet, if you run:
easy_install -U Pylons==dev

It has no problem fetching the latest Pylons and the Paste prereqs  
(which would have the same problem if I hadn't linked to them  
explicitly on the Pylons page).

Since you already indicate you want ==dev, shouldn't it keep that  
during the prereq if necessary?

- Ben