Revert "Revert "Reset the wakeup timeout when we re-enter the continue wait.""

This reverts commit 82a38837.

The original version had a copy-paste error: using the Interrupt timeout
for the ResumeSynchronous wait, which is clearly wrong.  This error would
have been evident with real use, but the interrupt is long enough that it
only caused one testsuite failure (in the Swift fork).

Anyway, I found that mistake and fixed it and checked all the other places
where I had to plumb through a timeout, and added a test with a short
interrupt timeout stepping over a function that takes 3x the interrupt timeout
to complete, so that should detect a similar mistake in the future.