Code review comment for lp:~henninge/launchpad/bug-458924

= Details =
See bug 458924.
This is a simple improvement to FakeTime. I thought that with these improvements I could use FakeTime instead of some local implementations in my tests but I found that lp.testing.time_counter is more what I need. Still, I think this improvement to FakeTime might be useful anyway.

== Test ==
All tests currently using FakeTime should still pass. They are found in codehosting.

bin/test -vvct TestBranchRewriter -t TestLoggingUIFactory -t TestBranchFileSystemClient

= Launchpad lint =
I did *not* fix the imports because this is an __init__.py file and people might be importing from here.

Checking for conflicts. and issues in doctests and templates.
Running jslint, xmllint, pyflakes, and pylint.
Using normal rules.

Linting changed files:
  lib/lp/testing/__init__.py

== Pyflakes notices ==

lib/lp/testing/__init__.py
    20: 'InvalidURLJoin' imported but unused
    43: 'is_logged_in' imported but unused
    45: 'test_tales' imported but unused