Get the status for a submodule.
This looks at a submodule and tries to determine the status. It
will return a combination of the GIT_SUBMODULE_STATUS
values above.
How deeply it examines the working directory to do this will depend
on the git_submodule_ignore_t
value for the submodule.
Combination of GIT_SUBMODULE_STATUS
flags
name of the submodule
0 on success, < 0 on error