Refactor list of of repo-local env vars

Move the list of GIT_* environment variables that are local to a
repository into a static list in environment.c, as it is also
useful elsewhere. Also add the missing GIT_CONFIG variable to the
list.

Make it easy to use the list both by NULL-termination and by size;
the latter (excluding the terminating NULL) is stored in the
local_repo_env_size define.

Signed-off-by: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

environment.c

@@ -63,6 +63,23 @@ static char *work_tree;
 static const char *git_dir;
 static char *git_object_dir, *git_index_file, *git_refs_dir, *git_graft_file;
 
+/*
+ * Repository-local GIT_* environment variables
+ * Remember to update local_repo_env_size in cache.h when
+ * the size of the list changes
+ */
+const char * const local_repo_env[LOCAL_REPO_ENV_SIZE + 1] = {
+	ALTERNATE_DB_ENVIRONMENT,
+	CONFIG_ENVIRONMENT,
+	DB_ENVIRONMENT,
+	GIT_DIR_ENVIRONMENT,
+	GIT_WORK_TREE_ENVIRONMENT,
+	GRAFT_ENVIRONMENT,
+	INDEX_ENVIRONMENT,
+	NO_REPLACE_OBJECTS_ENVIRONMENT,
+	NULL
+};
+
 static void setup_git_env(void)
 {
 	git_dir = getenv(GIT_DIR_ENVIRONMENT);