- adserve.inc

    o support multiple arguments when invoking function in file
    o simplify code by using _debug_echo() when possible
    o support caches with adserve hooks
 - ad_cache_file.inc
    o simplify code by using _debug_echo() when possible
    o preface debug calls with 'File cache:' to make tracing more clear
    o make cache data re-usable without having to reload it
    o introduce adserve_select hook
    o set sane file cache defaults