swift-mock: better name for Swift mock

We will be moving the client-side code out of this file and call that
code a Swift simulator.
swift-simulator: move code out of swift-mock (fixes #59)

This makes it possible to debug the code in the simulator: the code is
loaded using a script element during testing and this makes it
possible to set breakpoints like normal when the browser is paused
with a call to browser.pause() in a test.
swift-mock: move JSON wrapping out of swift-simulator
Merge pull request #70 from mgeisler/swift-mock

Push swift simulator code into client-side script
swift-simulator: correct handling of prefix

Before, a request with prefix=foo and an object named foo/bar.txt
would result in '/bar.txt' being returned.

This is incorrect since Swift really returns 'foo/' in that case. In
general, objects and subdirs are always returned using their full
name, so we should not cut off the prefix like we did.