fix(plug-in): handle unintentional source includes

This commit handles unintentional source includes by hijacking the
browserify exposeAll=true option. This ensures all files get exported
through the generated bundle.

Individual files are then properly recognized by test stubs AND via
direct (in-bundle) lookup.

Unfortunately this breaks external requires, e.g.
`browserify.external('foobar')`. Oooops!

Failing test case attached.

Related to #52