[Distutils] Changes to --find-links and --upgrade in SVN

[Phillip J. Eby]

Elvelind Grandin reported a problem with the "develop" command that turned 
out to be a flaw in its --find-links support.  Specifically, it wasn't ever 
processing the links.  :)

In the process of fixing it, I wound up cleaning up an annoying (to me, at 
least) quirk of the previous workings of --find-links.  It used to be that 
find-links would always be processed first, no matter what, even if you 
were doing a completely local operation.  This would've been especially 
annoying if it carried over into "develop", so I made some changes.

Now, if an item passed to --find-links is local (a filename or file: URL), 
or a direct link to an egg or other distribution, it is indexed 
immediately.  Remote URLs are now only retrieved if a dependency can't be 
resolved locally, or if you use the -U or --upgrade options (this goes for 
"develop" too).

Note that this is a behavior change for easy_install, which was effectively 
treating --find-links as though you'd specified --upgrade in certain 
cases.  So, if you're used to getting upgrades downloaded as a result of 
using --find-links, please note that this will no longer 
happen.  EasyInstall will now *only* go online if a dependency can't be 
resolved locally, if -U or --upgrade is used, or if you provided suitable 
direct URLs via an argument or --find-links, or via a link in a local .html 
file.