git bisect/checkout and changes to .gitignore

[Chris Angelico <rosuav@gmail.com>]

Greetings! I'm not certain if this list or the git-users group is more
appropriate; my apologies if I've picked wrong.

At my workplace we use git to manage all of our source code. Every now
and then, we decide that some particular file oughtn't to be
git-managed, and add it into .gitignore and remove it from the
repository (for instance, configuration files that become
per-developer).

Is there a way to checkout an old version of the repository (before
the file was added to .gitignore), then return to the current state,
without destroying these sorts of files? Currently, checking out the
old version quietly "takes control" of the file, and then checking out
a newer one deletes it.

I've read through the man pages for 'git checkout' and 'gitignore' and
searched the one for 'git config' (it's a little large to read all
of), without seeing an option to preserve files on checkout. Is there
a way to do this, and if so, where can I find it?

Thanks in advance!

Chris Angelico