scmutil: use context managers for file handles Now that we dropped support for Python 2.4, we are able to use context managers. Let's replace the try..finally pattern in scmutil.py with context managers, which close files automatically when the context manager is exited. There should be no change in behavior with this patch. Why convert to context managers if nothing is broken? I'm working on closing file handles in background threads to improve performance on Windows. As part of this, I realized there could be some future issues if the background file closing code isn't designed with context managers in mind. So, I'd like to switch some code to context managers so I can design an API that works with context managers.