Merge branch 'ab/complete-show-all-commands'

The command line completion script (in contrib/) learned to complete all Git subcommands, including the ones that are normally hidden, when GIT_COMPLETION_SHOW_ALL_COMMANDS is used. * ab/complete-show-all-commands: completion: add a GIT_COMPLETION_SHOW_ALL_COMMANDS completion tests: re-source git-completion.bash in a subshell