use strbuf_addstr() for adding constant strings to a strbuf

Replace uses of strbuf_addf() for adding strings with more lightweight
strbuf_addstr() calls.

In http-push.c it becomes easier to see what's going on without having
to verfiy that the definition of PROPFIND_ALL_REQUEST doesn't contain
any format specifiers.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rev-parse.c

@@ -469,7 +469,7 @@ static int cmd_parseopt(int argc, const char **argv, const char *prefix)
 			(stop_at_non_option ? PARSE_OPT_STOP_AT_NON_OPTION : 0) |
 			PARSE_OPT_SHELL_EVAL);
 
-	strbuf_addf(&parsed, " --");
+	strbuf_addstr(&parsed, " --");
 	sq_quote_argv(&parsed, argv, 0);
 	puts(parsed.buf);
 	return 0;