Merge branch 'jc/maint-config-exit-status'

Merge branch 'jc/maint-config-exit-status'

The exit status code from "git config" was way overspecified while
being incorrect.  Update the implementation to give the documented
status for a case that was documented, and introduce a new code for
"all other errors".

* jc/maint-config-exit-status:
  config: "git config baa" should exit with status 1