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>

config.h

@@ -169,16 +169,18 @@ int git_default_config(const char *, const char *,
 int git_config_from_file(config_fn_t fn, const char *, void *);
 
 int git_config_from_file_with_options(config_fn_t fn, const char *,
-				      void *,
+				      void *, enum config_scope,
 				      const struct config_options *);
 int git_config_from_mem(config_fn_t fn,
 			const enum config_origin_type,
 			const char *name,
 			const char *buf, size_t len,
-			void *data, const struct config_options *opts);
+			void *data, enum config_scope scope,
+			const struct config_options *opts);
 int git_config_from_blob_oid(config_fn_t fn, const char *name,
 			     struct repository *repo,
-			     const struct object_id *oid, void *data);
+			     const struct object_id *oid, void *data,
+			     enum config_scope scope);
 void git_config_push_parameter(const char *text);
 void git_config_push_env(const char *spec);
 int git_config_from_parameters(config_fn_t fn, void *data);