package versions

[ongardie]

Most of the packages currently download/build the latest stable release. That's usually what you want, but sometimes you need an older version for compatibility or a newer version for bleeding edge testing. Ideally, most packages would be able to build different versions.

Another complication is installing multiple versions at the same time. Lots of the current packages could have multiple versions co-exist relatively easily, but we usually need to be able to express a single "default".

A related question is package "features" (or USE flags).