The parsing for the output of `git config --list` is the same for
both the global options and the current repository's options so we
can really just use the same parser between them.

I'm currently just refactoring the parser so we can use a different
one depending on the version of git available to us at runtime.  My
next change will add support for 1.5.3's --null option.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>