Add the concept of a “precious” file (ignored but not to be “cleaned” away)

[LemmingAvalanche]

A precious file is a special kind of ignored file:

• Untracked and ignored
• Not deleted by commands like git clean -fdx

The idea is that some files are not tracked by the project but is useful to the user. Like the .idea directory (Intellij configuration).

From https://lore.kernel.org/git/xmqqttqytnqb.fsf@gitster.g/T/#m8cc303540c72c3b8f80c8e21dec5fb0acd8253a0

See also (2011) https://lore.kernel.org/git/7vipsnar23.fsf@alter.siamese.dyndns.org/

[LemmingAvalanche]

Current email threads on this topic can be found by searching for precious-files.txt.

[dscho]

Current email thread is here: https://lore.kernel.org/git/pull.1627.git.1703643931314.gitgitgadget@gmail.com/#r