skip adding the key to metadata, if it would be an empty arrayref
provide config data for [MetaConfig]
when git has not been configured, git dies

e.g.  http://www.cpantesters.org/cpan/report/b0b2818c-1a07-11e4-bb80-392474eb9bac
pull all the repetitive boilerplate out to a helper library
warn at runtime if Pod::Weaver::Section::Contributors version <= 0.007
display any warnings we received from git
reuse the variable we already populated
if run in a directory where git init has not been run, we were exploding

e.g.:

    fatal: ambiguous argument 'HEAD': unknown revision or path not in the working tree.
    Use '--' to separate paths from revisions, like this:
    'git <command> [<revision>...] -- [<file>...]
Dist-Zilla-Plugin-Git-Contributors-0.002

          - do not add an empty x_contributors key if there are no
            (non-author) contributors to report
          - fix test failures when run on a system where git has not been
            configured
          - warn at runtime if Pod::Weaver::Section::Contributors is too old
            to pull data from distmeta on its own
          - do not blow up if run in a directory that is not tracked by git