freetype:
 * add missing zlib-dependency
 * expected to fix build problem reported in [http://www.ip-phone-forum.de/showthread.php?t=261035 this thread]
 * refs #2072


git-svn-id: file:///var/svn/freetz/trunk@10844 149334a1-2f27-0410-a3b9-fc62619ac1e6