Cleaned up tests; added additional test
Changed prop name for clarification, changed method

Note: This commit exposes a bug in .owns--namely, that it doesn't do what it says
it does. No surprise, really, as no tests are yet written for .owns. I'll resolve
both in a subsequent commit.
Added test for, fixed proxies' .owns method
Added, refined _.isAncestor tests
Added test for, patched hole in isAncestor fn