fix mod_unique_id to work with 64-bit time_t

Submitted by:	Alvaro Martinez Echevarria <alvaro-httpd@lander.es>


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@81496 13f79535-47bb-0310-9956-ffa450edef68