Allow eunit test to access to project's priv_dir.

I'm not sure how to reproduce the issue some people experienced
(OS, make version maybe? who knows) but I got a report that this
fixes it. It's also definitely the "right" way to do this.

Also includes a fix for multi-application repositories.

This commit implements a core_find and core_ls function that
can be used to list files recursively or not.

A few other minute changes are included and a couple hacks
removed.

Rebased and moved ct.cover.spec into the test/ directory.

There is no value in a verbose mode for eunit by default because
eunit will print errors of failing tests regardless of what mode
is used. Verbose mode only seem to output what modules are tested
and what tests pass in those modules, in addition to errors.

Disabling verbose will make errors much easier to notice.