This can be overridden to allow session-based temporary file management
By default, all files are deleted at the end of a session. The web installer needs to be able to sustain a list over many sessions in order to support user interaction with install scripts
Parameters:
Set the frontend class that will be used by calls to singleton()
Frontends are expected to conform to the PEAR naming standard of _ => DIRECTORY_SEPARATOR (PEAR_Frontend_CLI is in PEAR/Frontend/CLI.php)
Parameters: