further updates to config_cascade patch

- add mediameta and license config files into the cascade
- update the cache validity code in cache.php, css.php & js.php to use config_cascade
- redo inclusion of main config files to avoid suppression of errors in config files
- add getConfigFiles($type) function
- minor updates elsewhere to use config_cascade rather than hardcoded config file names

darcs-hash:20090122114457-f07c6-98ad5627fd5df93edf8dd03289b9cf6d81962afe.gz