Changing elogind IPCRemove default.

[Mark Hindley]

Hello colleagues,

In bug #949698, the reporter is demanding that we change the default for
IPCRemove from true to false so that /dev/shm is not cleared on user logout.
This is essential for his usage. See man logind.conf(5) for further details. The
default is inherited from systemd.

I would like opinions on the wider implications of making this change.

Thanks.

Mark