R1:1c62a35710e5

Run one daemon to pull all working copies, not one daemon per working copy

Summary:
Allow the pull daemon to take a list of repositories. By default, pull all repositories.

Make some effort to respect pull frequencies, although we'll necessarily suffer a bit if running with only one process.

NOTE: We still launch one discovery daemon per working copy, so this only cuts the daemon count in half.

Test Plan:
- Ran `phd debug pulllocal`, verified behavior.
- Ran `pull.php P MTEST SVNTEST --trace`…