add a library of timeval manipulation functions, and change a large number of usses to use the new functions (bug #4504)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@6146 65c4cc65-6c06-0410-ace0-fbb531ad65f3

cdr/cdr_csv.c

@@ -123,7 +123,7 @@ static int append_date(char *buf, struct timeval tv, size_t bufsize)
 	t = tv.tv_sec;
 	if (strlen(buf) > bufsize - 3)
 		return -1;
-	if (!tv.tv_sec && !tv.tv_usec) {
+	if (ast_tvzero(tv)) {
 		strncat(buf, ",", bufsize - strlen(buf) - 1);
 		return 0;
 	}