Re: [RFC/PATCH 6/8] config: add core.untrackedCache

Current state of affairs:

 * Enable on a per-repo basis: git update-index --untracked-cache
 * Disable on a per-repo basis: git update-index --no-cache
 * Enable system-wide: N/A
 * Disable system-wide: N/A

With this patch:

 * Enable on a per-repo basis: git update-index --untracked-cache OR
"git config core.untrackedCache true"
 * Disable on a per-repo basis: git update-index --no-cache OR "git
config core.untrackedCache false"
 * Enable system-wide: git config --global core.untrackedCache true
 * Disable system-wide: git config --global core.untrackedCache false
 * Caveat: The core.untrackedCache config has precidence over "git update-index"

With the rest of the patches in this series:

 * Enable system-wide & per-repo the same, just tweak
core.untrackedCache either for the local .git or --globally
 * If you want to test things either per-repo or globally just use
"git update-index --test-untracked-cache"
 * If you want something exactly like the old --untracked-cache do:
"git update-index --test-untracked-cache && git config
core.untrackedCache true"

I think applying this whole series makes sense. Enabling this feature
doesn't work like anything else in Git, usually you just tweak a
config option and thus can easily enable things either system-wide or
per-repo (or any combination of the two), which makes both system
administration and local configuration easy.

A much saner UI for the CLI tools if we're going to ship git with
tests for filesystem features is to separate the testing from the
enabling of those features.

My spontanous feeling: squash 6-8 together and add this nice explanation
to the commit message.