cleanup: use the deque type where appropriate
There have been quite a few places where we pop elements off the
front of a list. This can turn O(n) algorithms into something more
like O(n**2). Python has provided a deque type that can do this
efficiently since at least 2.4.
As an example of the difference a deque can make, it improves
perfancestors performance on a Linux repo from 0.50 seconds to 0.36.
To run the tests, do:
cd tests/
python run-tests.py
See http://mercurial.selenic.com/wiki/WritingTests for
more information on writing tests.