We were only pulling in autoloads files for packages installed via
packages.el. This was not that noticeable because all pinned packages
without custom derivations end up installed that way, but it does affect
extra packages (including the one pointed out in #11).
Try to fix this by including autoloads files in the top-level site-lisp
directory from emacsWithPackages.
They do not have src set, so if we pull them in without having a pin
they fail to build.
Noticed with org, so add a test for that. Probably not the only one
affected, though.
Fixes#4
