don't use the export global for imports

Previously if exporting to `foo`, all imports would be expected to be on `foo`, even with the `imports` options specified, making it impossible to import pretty much anything when using the `global` option.

I considered using `window` on all imports, but if something is truly global you shouldn't need that. Additionally, in some environments you wouldn't have `window`. I realize it is unlikely to be used anywhere but a browser, but this still works in browsers and consumers can configure an `import` to add `window` or `this` if needed.