Merge branch 'pb/complete-config'

The command line completion script (in contrib/) learned to complete configuration variable names better. * pb/complete-config: completion: add and use __git_compute_second_level_config_vars_for_section completion: add and use __git_compute_first_level_config_vars_for_section completion: complete 'submodule.*' config variables completion: add space after config variable names also in Bash 3