Provide git_config with a callback-data parameter

git_config() only had a function parameter, but no callback data
parameter.  This assumes that all callback functions only modify
global variables.

With this patch, every callback gets a void * parameter, and it is hoped
that this will help the libification effort.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin-commit.c b/builtin-commit.c
index a65c2b8..9f0026e 100644
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -773,7 +773,7 @@
 	const char *index_file;
 	int commitable;
 
-	git_config(git_status_config);
+	git_config(git_status_config, NULL);
 
 	if (wt_status_use_color == -1)
 		wt_status_use_color = git_use_color_default;
@@ -827,7 +827,7 @@
 	}
 }
 
-int git_commit_config(const char *k, const char *v)
+int git_commit_config(const char *k, const char *v, void *cb)
 {
 	if (!strcmp(k, "commit.template")) {
 		if (!v)
@@ -836,7 +836,7 @@
 		return 0;
 	}
 
-	return git_status_config(k, v);
+	return git_status_config(k, v, cb);
 }
 
 static const char commit_utf8_warn[] =
@@ -864,7 +864,7 @@
 	unsigned char commit_sha1[20];
 	struct ref_lock *ref_lock;
 
-	git_config(git_commit_config);
+	git_config(git_commit_config, NULL);
 
 	argc = parse_and_validate_options(argc, argv, builtin_commit_usage);