* tests: Run tests with the amalgamated xonsh
* tests: Test xonsh loads correctly interactively
* tests: Ensure tests run from amalgamated xonsh
* environ: Separate $XONSH_DEBUG and $XONSH_NO_AMALGAMATE
* tests: Keep XONSH_NO_AMALGAMATE in a comment for ease of debugging
* tests: Fix monkeypatch for amalgamated code
