Release 6.18.2: default UPLOAD_DIRECTORY moved to /var/spool/open-xchange/uploads

[changerequest]

Depending on the distribution and the system settings, the /tmp directory will be cleaned on a regular base. This does not work for UPLOAD_DIRECTORY in Open-Xchange and thus, the default will now be changed to /var/spool/open-xchange/uploads.

Existing installations will not be affected by this change, which means, it will not be changed with an update.