StubTreq does not support the timeout argument

[twm]

There are two related issues here:

1. StubTreq doesn't accept a reactor, so there's no way for the caller to manipulate time.
2. StubTreq doesn't pass that reactor when it instantiates HTTPClient, so HTTPClient uses the global reactor to set the timeout.

Thus, if the timeout argument is passed to StubTreq.get() et. al. a delayed call is registered in the global reactor.