Allow user additions to /etc/sysconfig/lm_sensors

[khali]

It could be useful to let the user add custom modules to /etc/sysconfig/lm_sensors. Unfortunately, sensors-detect overwrites /etc/sysconfig/lm_sensors when run, so this isn't possible. We should change sensors-detect to update /etc/sysconfig/lm_sensors instead of overwriting it. Then we could define a variable in that file (for example EXTRA_MODULES) where the user could list additional kernel modules to be loaded for the lm_sensors service. Lastly, initialization scripts would have to be updated to handle this new variable.

Discussion at:
 http://lists.lm-sensors.org/pipermail/lm-sensors/2009-January/025200.html