Merge branch 'mm/config-edit-global'

Start "git config --edit --global" from a skeletal per-user
configuration file contents, instead of a total blank, when the
user does not already have any.  This immediately reduces the need
for a later "Have you forgotten setting core.user?" and we can add
more to the template as we gain more experience.

* mm/config-edit-global:
  commit: advertise config --global --edit on guessed identity
  home_config_paths(): let the caller ignore xdg path
  config --global --edit: create a template file if needed

path.c

@@ -148,10 +148,12 @@ void home_config_paths(char **global, char **xdg, char *file)
 			*global = mkpathdup("%s/.gitconfig", home);
 	}
 
-	if (!xdg_home)
-		*xdg = NULL;
-	else
-		*xdg = mkpathdup("%s/git/%s", xdg_home, file);
+	if (xdg) {
+		if (!xdg_home)
+			*xdg = NULL;
+		else
+			*xdg = mkpathdup("%s/git/%s", xdg_home, file);
+	}
 
 	free(to_free);
 }