We now install a post-checkout git hook as part of prepare-dev.py

that will remove all .pyc files in the repository when a new ref is

checked out. This is to prevent stale .pyc files from other release

branches from sticking around when working on patches on multiple

versions of Review Board (without having to provide instructions on

setting up multiple git worktrees to developers).

Ran ./contrib/internal/prepare-dev.py and observed the following:

if the hook did not exist it would be created;
if the hook did exist but didn't match the content a warning was

  printed; and
if the hook did exist but was non-executable it was overwritten.