Make mce_gconf_notifier_remove() friendlier for normal uses

No need to litter code with GPOINTER_TO_INT() and dummy parameters
just to make the function compatible with g_slist_foreach()

Add separate helper function mce_gconf_notifier_remove_cb() for the
one exceptional case that actually uses g_slist_foreach().

Also make sure mce_gconf_notifier_add() always sets the resulting
notification id before returning to the caller and allow calling
mce_gconf_notifier_remove() with zero id without ill effects.
Do not exit / disable plugins if builtin gconf keys are missing

In general all configurable items have sane built-in defaults and
thus not having configuration keys available must not result in
termination of mce process or rejecting loaded plugins.

Since unwanted exits have been removed, mce_gconf_notifier_add()
can now return actual success/failure value - except for the
gconf disabled on purpose situation.

Also normalize places where mce_gconf_notifier_add() is used so that
initial value is read after installing change notifier callback.
Suppress warnings about missing led configuration toggles

Since custom led patterns can be added via ini-files and enable/disable
configuration deals with default patterns only, mce should not complain
about missing led configuration keys by default.

[mce] Suppress warnings about missing led configuration toggles. Fixes JB#20539
Update power up brightness when starting display state transition

The power up brightness was evaluated too late and caused jumps in
brightness during unblanking. Possible went unnoticed until changes
to ambient light sensor power up were made to accommodate the proximity
based lpm display states.

[mce] Update power up brightness when starting display state transition. Fixes JB#20590
Merge pull request #183 from spiiroin/unblank_brightness

Update power up brightness when starting display state transition
Bump mce version to 1.31.8
Merge pull request #181 from spiiroin/led_config_toggles

Led config toggles
Bump mce version to 1.31.9