This is an ugly chunk of code, so let's put it into its own function.

If the remote is anonymous, then we cannot check for any configuration,
as there is no name. Check for this before we try to use the name, which
may be a NULL pointer.

This fixes #2697.

This reduces the clutter somewhat and lets us see what we're asking
about the reference.

This gets the value from branch.<foo>.remote.

We cannot know from looking at .gitmodules whether a directory is a
submodule or not. We need the index or tree we are comparing against to
tell us. Otherwise we have to assume the entry in .gitmodules is stale
or otherwise invalid.

Thus we pass the index of the repository into the workdir iterator, even
if we do not want to compare against it. This follows what git does,
which even for `git diff <tree>`, it will consider staged submodules as
such.

ignore: don't leak rules into higher directores

Threading and crypto libraries

remote: check for the validity of the refspec when updating FETCH_HEAD