[Twisted-Python] Intended semantics of IReactorTime.seconds

Currently, as far as I can tell, all implementations of `IReactorTime.seconds()` (excluding twisted.internet.task.Clock, obviously) are just `time.time()`; IOW, the return value is the number of seconds since the beginning of the UNIX epoch in UTC. Are these the intended semantics? The interface docstring doesn't really make this clear at all. There's some commented out code which suggests the implementation used to be `time.clock()` on win32, which would not satisfy these semantics. (The background for this question is that I'm writing some code which takes an IReactorTime provider for testing purposes, and I'm wondering if I need a separate provider of `datetime.now()` functionality or not)