Release 2014.8
treecompose: Remove internal caching, require --repo argument

It's a lot clearer if the inputs, outputs, and cache state are cleanly
separated.  At least the "lorax" tool relies on a local HTTP cache
instead of keeping around the yum repos - let's do the same.

This commit causes treecompose to require a --repo argument, and it
also gains an optional --proxy argument.
core: Remove src/autobuilder

This will move to a separate repository.  This allows a clearer
separation between the core tool (which is shipped on client systems
too), and the compose infrastructure.

Furthermore, I want to make the autobuilder a Docker container.