Merge branch 'ua/some-builtins-wo-the-repository'

A handful of built-in command implementations have been rewritten to use the repository instance supplied by git.c:run_builtin(), its caller. * ua/some-builtins-wo-the-repository: builtin/checkout-index: stop using `the_repository` builtin/for-each-ref: stop using `the_repository` builtin/ls-files: stop using `the_repository` builtin/pack-refs: stop using `the_repository` builtin/send-pack: stop using `the_repository` builtin/verify-commit: stop using `the_repository` builtin/verify-tag: stop using `the_repository` config: teach repo_config to allow `repo` to be NULL