dir.c: free "ident" and "exclude_per_dir" in "struct untracked_cache"
When the "ident" member of the structure was added in 1e8fef609e7 (untracked cache: guard and disable on system changes, 2015-03-08) this function wasn't updated to free it. Let's do so. Let's also free the "exclude_per_dir" memory we've been leaking since[1], while making sure not to free() the constant ".gitignore" string we add by default[2]. As we now have three struct members we're freeing let's change free_untracked_cache() to return early if "uc" isn't defined. We won't hand it to free() now, but that was just for convenience, once we're dealing with >=2 struct members this pattern is more convenient. 1. f9e6c649589 (untracked cache: load from UNTR index extension, 2015-03-08) 2. 039bc64e886 (core.excludesfile clean-up, 2007-11-14) Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Taylor Blau <me@ttaylorr.com>