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/http.c b/http.c
index acf746a..2a21ccb 100644
--- a/http.c
+++ b/http.c
@@ -90,7 +90,7 @@
 }
 #endif
 
-static int http_options(const char *var, const char *value)
+static int http_options(const char *var, const char *value, void *cb)
 {
 	if (!strcmp("http.sslverify", var)) {
 		if (curl_ssl_verify == -1) {
@@ -169,7 +169,7 @@
 	}
 
 	/* Fall back on the default ones */
-	return git_default_config(var, value);
+	return git_default_config(var, value, cb);
 }
 
 static CURL* get_curl_handle(void)
@@ -263,7 +263,7 @@
 	if (low_speed_time != NULL)
 		curl_low_speed_time = strtol(low_speed_time, NULL, 10);
 
-	git_config(http_options);
+	git_config(http_options, NULL);
 
 	if (curl_ssl_verify == -1)
 		curl_ssl_verify = 1;