Merge branch 'cc/untracked'
Update the untracked cache subsystem and change its primary UI from
"git update-index" to "git config".
* cc/untracked:
t7063: add tests for core.untrackedCache
test-dump-untracked-cache: don't modify the untracked cache
config: add core.untrackedCache
dir: simplify untracked cache "ident" field
dir: add remove_untracked_cache()
dir: add {new,add}_untracked_cache()
update-index: move 'uc' var declaration
update-index: add untracked cache notifications
update-index: add --test-untracked-cache
update-index: use enum for untracked cache options
dir: free untracked cache when removing it