[PATCHES BUG 13865] memcache tracking of talloc object sizes

[Christof Schmitt]

This is a fix for memcache to also add the talloc object size to the
amount of used space. The objects become part of the memcache, so the
sizes should be tracked as well.

The third patch is a clarification to the description of the 'max stat
cache size' parameter.

Pipeline is running at:
https://gitlab.com/samba-team/devel/samba/pipelines/54120627

Christof