Improve support for the file protocol

[matthewp]

This change improves support for using the file protocol with page.js.
Basically once you enable hashbang we treat the base as though it were
/. Fixes #209

[coveralls]

Coverage increased (+0.1%) to 90.0% when pulling 12e0189 on file-protocol into 1269035 on master.

[coveralls]

Coverage increased (+0.1%) to 90.0% when pulling 17e2695 on file-protocol into 1269035 on master.

[kaisermann]

@matthewp Sorry for commenting on an old PR, but could you explain what the location.protocol check here does in this context? I'm trying to save the last scroll position on page.exit (by using ctx.save) but my apps use the file: protocol and I'm unable to modify (and save) the current context before going to another one.

Edit: please tell me if this is not the right way to do this 😁