Merge branch 'sb/submodule-cleanup-export-git-dir-env'

Code cleanup.

* sb/submodule-cleanup-export-git-dir-env:
  submodule.c: use GIT_DIR_ENVIRONMENT consistently

submodule.c

@@ -1379,7 +1379,8 @@ void prepare_submodule_repo_env(struct argv_array *out)
 		if (strcmp(*var, CONFIG_DATA_ENVIRONMENT))
 			argv_array_push(out, *var);
 	}
-	argv_array_push(out, "GIT_DIR=.git");
+	argv_array_pushf(out, "%s=%s", GIT_DIR_ENVIRONMENT,
+			 DEFAULT_GIT_DIR_ENVIRONMENT);
 }
 
 /*