t/10-no-global-git.t: Test failure of ~/.gitconfig not being set up.

If you have no git.user in ./.git/config and no git.user in ~/.gitconfig,
calling ->_releaser causes git to fatalize in a very unfriendly way
without any context.

Additional Fixes After rebasing:

  Initially used Test::Differences, scrapped.
  Unicode magic nuked.
  Better comments and documentation.
  local localises all the things instead of only some of them.
  remove metaconfig
  test renamed
Contributors.pm: For _releaser, excute git.config in a try { } block to avoid fataling.

As it is, if there is no user.name anywhere ( either in ~ or ./ ), git
fatalizes.
Contributors.pm: Avoid warning about undef eq $value when $releaser is undef.

Only perform the releaser filter if a releaser is defined.
.mailmap: Add kentnl@cpan.org for future glory.
Update changes