config: pass ctx with config files

Pass config_context to config_callbacks when parsing config files. To
provide the .kvi member, refactor out the configset logic that caches
"struct config_source" and "enum config_scope" as a "struct
key_value_info". Make the "enum config_scope" available to the config
file machinery by plumbing an additional arg through
git_config_from_file_with_options().

We do not exercise ctx yet because the remaining current_config_*()
callers may be used with config_with_options(), which may read config
from parameters, but parameters don't pass ctx yet.

Signed-off-by: Glen Choo <chooglen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

submodule-config.c

@@ -606,7 +606,7 @@ static const struct submodule *config_from(struct submodule_cache *cache,
 	parameter.gitmodules_oid = &oid;
 	parameter.overwrite = 0;
 	git_config_from_mem(parse_config, CONFIG_ORIGIN_SUBMODULE_BLOB, rev.buf,
-			config, config_size, &parameter, NULL);
+			    config, config_size, &parameter, CONFIG_SCOPE_UNKNOWN, NULL);
 	strbuf_release(&rev);
 	free(config);
 
@@ -714,7 +714,8 @@ void gitmodules_config_oid(const struct object_id *commit_oid)
 
 	if (gitmodule_oid_from_commit(commit_oid, &oid, &rev)) {
 		git_config_from_blob_oid(gitmodules_cb, rev.buf,
-					 the_repository, &oid, the_repository);
+					 the_repository, &oid, the_repository,
+					 CONFIG_SCOPE_UNKNOWN);
 	}
 	strbuf_release(&rev);