path for phpfastcache files backend is not detected correctly when running with nginx

The files plugin does not explicitly set the path where phpfastcache should create the cache files. If memcached is not available phpfastcache will fallback to its files driver.

When running on apache the path is set to /tmp/, which works, but is not optimal.
On nginx the path is set to /usr/share/kopano-webapp/../. This does not work because of permissions and is completely wrong, too.

This can be easily fixed by setting the cache path explicitly to, e.g /var/lib/kopano-webapp/tmp/filescache/ in /usr/share/kopano-webapp/plugins/files/php/lib/phpfastcache/phpfastcache.php.

This folder maybe needs chmod 777.

This should also be configurable in files config.php.

Testcase:

• create a directory mkdir -p /var/lib/kopano-webapp/plugin_files
• chown it to the webservers user and group e.g. chown www-data:www-data /var/lib/kopano-webapp/plugin_files
• use the files browser in webapp and open an account to show files and folders
• observe if files are created in that directory
• important do not have memcached installed!