buildProduction: Removed require.js-related workarounds that aren't necessary as of assetgraph@dc26103d.
Updated test so it doesn't depend on UglifyJS picking a particular mangled variable name.
Added orphaned require.js test.
Made buildProduction test immune to UglifyJs randomness.
Update assetgraph to 1.6.0beta13.
Release 1.8.0beta15.