Merge branch 'jk/startup-info' into maint

Merge branch 'jk/startup-info' into maint

The startup_info data, which records if we are working inside a
repository (among other things), are now uniformly available to Git
subcommand implementations, and Git avoids attempting to touch
references when we are not in a repository.

* jk/startup-info:
  use setup_git_directory() in test-* programs
  grep: turn off gitlink detection for --no-index
  mailmap: do not resolve blobs in a non-repository
  remote: don't resolve HEAD in non-repository
  setup: set startup_info->have_repository more reliably
  setup: make startup_info available everywhere