Support d.o release node URLs when installing new code, not just links to .tar.gz files directly

This might be won't fix, but the idea occurred to me and I thought it was at least worthy of discussion. ;) Following up from #606180: Add better validation and errors when installing new code via update manager, if a user is confused about what URL they're supposed to give the Update manager to install a new project, and uses something like:

http://drupal.org/node/608852

instead of:

http://ftp.drupal.org/files/projects/views-7.x-3.x-dev.tar.gz

they get the following error:

"Cannot extract temporary://update-cache/608852, not a valid archive."

Not so helpful. :(

It's probably bloat, and perhaps a terrible idea, but in this case, we could recognize it's a d.o/node/* URL, see if it looks like a release node, and if so, extract the .tar.gz URL from it and download that for them... We'd want to be careful to do so in a way that doesn't lock us in to the design and layout of release nodes. Maybe d.o release nodes should embed this info in a special HTML comment so that we can just look for that, instead of parsing the visual HTML.

Thoughts? ;)