`make distclean` doesn't remove everything

Running a `make distclean` in a checkout of Apache CouchDB from git should remove all dependencies in other repos, including:
* config
* b64url
* ets_lru
* khash
* snappy
* docs
* fauxton
* folsom
* hyper
* ibrowse
* jiffy
* mochiweb
* meck
* recon
* bear

It should also remove the `rel/couchdb` release folder, and any `apache-couchdb-...` dist tarball/folder.

In short, after running `make distclean`, the directory should look *exactly* like it would from a fresh clone.

In working on this, it would be acceptable for the `distclean` Makefile to shell out to commands like `git reset --hard` and `git clean -ffdx` but that's not sufficient to remove the external repo dependencies, since they're in `.gitignore`.

Start at the distclean target in the Makefile and review the listed external repositories, .gitignore, rel/couchdb, and apache-couchdb-... distribution artifacts. Verify that running make distclean removes those dependencies and artifacts so the checkout matches a fresh clone.

Written by the indexing model from the issue text.