This fixes the way that submodule status is checked to bypass just
about all of the caching in the submodule object. Based on the
ignore value, it will try to do the minimum work necessary to find
the current status of the submodule - but it will actually go to
disk to get all of the current values.
This also removes the custom refcounting stuff in favor of the
common git_refcount style. Right now, it is still for internal
purposes only, but it should make it easier to add true submodule
refcounting in the future with a public git_submodule_free call
that will allow bindings not to worry about the submodule object
getting freed from underneath them.
This is probably not the final form of this change, but this is
a preliminary version of checking a timestamp to see if the cached
working directory HEAD OID matches the current. Right now, this
uses the timestamp on the index and is, like most of our timestamp
checking, subject to having only second accuracy.
This is a big redesign of the git_submodule_status API and the
implementation of the redesigned API. It also fixes a number of
bugs that I found in other parts of the submodule API while
writing the tests for the status part.
This also fixes a couple of bugs in the iterators that had not
been noticed before - one with iterating when there is a gitlink
(i.e. separate-work-dir) and one where I was treating anything
even vaguely submodule-like as a submodule, more aggressively
than core git does.
