Make system lock world-readable

[blee]

Currently, conf_cleanExit requires a privileged call to check if the system is locked.

Now that *all* exits (clean or otherwise) happen with conf_cleanExit, this gets annoying:

blee@supra.b1c1l1 ~ $ sudo -k
blee@supra.b1c1l1 ~ $ confman version
confman-1.9.a (391)
Password: 

The system lock should be world-readable -- it doesn't contain any sensitive data.

[blee]

(In [449]) Ensure that lock files are world-readable, which removes the need for
conf_system_is_locked to use sudo.

See #80

[blee]

(In [450]) Merge from trunk world-readable locks.

Fixes #80