Merge branch 'jc/config-case-cmdline-take-2' into maint

The code to parse "git -c VAR=VAL cmd" and set configuration variable for the duration of cmd had two small bugs, which have been fixed. This supersedes jc/config-case-cmdline topic that has been discarded. * jc/config-case-cmdline-take-2: config: use git_config_parse_key() in git_config_parse_parameter() config: move a few helper functions up