http: fix some printf format warnings

Commit f8117f55 ("http: use off_t to store partial file size",
02-11-2015) changed the type of some variables from long to off_t.
Unfortunately, the off_t type is not portable and can be represented
by several different actual types (even multiple types on the same
platform). This makes it difficult to print an off_t variable in
a platform independent way. As a result, this commit causes gcc to
issue some printf format warnings on a couple of different platforms.

In order to suppress the warnings, change the format specifier to use
the PRIuMAX macro and cast the off_t argument to uintmax_t. (See also
the http_opt_request_remainder() function, which uses the same
solution).

Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
Signed-off-by: Jeff King <peff@peff.net>

http.c

@@ -1617,8 +1617,8 @@ struct http_pack_request *new_http_pack_request(
 	if (prev_posn>0) {
 		if (http_is_verbose)
 			fprintf(stderr,
-				"Resuming fetch of pack %s at byte %ld\n",
-				sha1_to_hex(target->sha1), prev_posn);
+				"Resuming fetch of pack %s at byte %"PRIuMAX"\n",
+				sha1_to_hex(target->sha1), (uintmax_t)prev_posn);
 		http_opt_request_remainder(preq->slot->curl, prev_posn);
 	}
 
@@ -1772,8 +1772,8 @@ struct http_object_request *new_http_object_request(const char *base_url,
 	if (prev_posn>0) {
 		if (http_is_verbose)
 			fprintf(stderr,
-				"Resuming fetch of object %s at byte %ld\n",
-				hex, prev_posn);
+				"Resuming fetch of object %s at byte %"PRIuMAX"\n",
+				hex, (uintmax_t)prev_posn);
 		http_opt_request_remainder(freq->slot->curl, prev_posn);
 	}