When a submodule "A", which has another submodule "B" nested within
it, is "absorbed" into the top-level superproject, the inner
submodule "B" used to be left in a strange state. The logic to
adjust the .git pointers in these submodules has been corrected.
* sb/submodule-recursive-absorb:
submodule absorbing: fix worktree/gitdir pointers recursively for non-moves
cache.h: expose the dying procedure for reading gitlinks
setup: add gentle version of resolve_git_dir