Accidentally introduced runtime dependency on package.el

[raxod502]

We need package.el for package-built-in-p at runtime, so we know whether or not to signal an error due to a missing package. Unfortunately, this means we now have a runtime dependency on package.el. I think the most amusing way to solve this problem is to persistently cache the complete list of built-in packages, and update the cache whenever we detect that the output of M-x emacs-version has changed.

[raxod502]

This would also fix the issue of all recipe repositories being cloned looking for a recipe for emacs.

[raxod502]

Amusing as my original idea might have been, it makes way more sense to just use finder-inf, which (it turns out) has a nice alist of all the packages that are considered "built-in".

There's now no dependency on package.el at any point, runtime or compile time.