When setting system-name to nil (should that be allowed?), Emacs forgets
how to delete the lock files '.#.*' and all subsequent startups complain
about lockups by old dead PIDs.

From what I get, either system-name should not be allowed to set as nil or
file locks should be still deleted on exists because they still have
usernames in the aliases.

GNU Emacs 24.3.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.8.2)
 of 2013-08-07 on -mnt-storage-buildroots-staging-x86_64-eric