use apr_off_t and APR_OFF_T_FMT (for portability to 64-bit off_t systems)

Submitted by: Jeff Trawick
Reviewed by: Greg Stein


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@88288 13f79535-47bb-0310-9956-ffa450edef68