`git_submodule` objects were already refcounted internally in case
the submodule name was different from the path at which it was
stored. This makes that refcounting externally used as well, so
`git_submodule_lookup` and `git_submodule_add_setup` return an
object that requires a `git_submodule_free` when done.
This removes the fetchRecurse compiler warnings and makes the
behavior match the other submodule options (i.e. the in-memory
setting can be reset to the on-disk value).
Any well-behaved program should write a descriptive message to the
reflog whenever it updates a reference. Let's make this more prominent
by removing the version without the reflog parameters.
