Instead of using apt_pkg.get_lock, use the wrapped lock
context manager to make sure the lock is always released
correctly at the end of the function / with block.

The old code would not release the lock if slist.read_main_list()
throws an exception.

It seems that for unknown reasons, the fetcher was not
released after commit() ended, although it should have
been out of references.

Rewrite the code to use an explicit lock context manager
instead, this avoids the need of attaching the lock to
the acquire object and makes the code easier to understand.

We have to wrap apt_pkg.FileLock in another class to raise
the expected exceptions, and we need to have only one instance
of that class in the cache, as we might nest locks within each
other (_fetch_archives called in commit), and FileLock counts
the number of locks in its instance.

Closes: #922416

This fixes tests on derivates that are not listed in data/, and
on new development versions of listed distributions - this also
has a negative effect though: We might miss some.

This function is needed after calling create_pin() with an
empty package name (creating a repository pin).

Fork for PureOS: Update git-buildpackage config: Set branches. Use purism/* namespace for release tags. Avoid use pristine-tar. Drop prebuild script. Drop export-dir.

Fork for PureOS: Set PureOS Maintainers as maintainer, leaving original as XSBC-Original-Maintainer.

This reverts commit c1063b61.

FileFd was not supposed to be copyable, but accidentally was,
which worked fine here, but caused crashes elsewhere, so the
implicit copy constructor was explicitly deleted recently, causing
this to FTBFS.

data/templates/Debian.info.in: Add Buster and Bullseye

See merge request apt-team/python-apt!14

Those fail to build due to not having a recent enough apt.

This makes pep8 work again.