Use a sensible second require_path
Revert "Refactor dependenct_gems to use map, not each"

The refactor commit was based on an inaccurate reading of
dependent_gems.  This restores the original along with a test to prevent
the same mistake from being made twice.

This reverts commit 485e2ddbb71a715d2cccdcbe75fa2e66d8308844.