log: defined value as an index-pointer after static slots
log: defined value as an index-pointer after static slots

Amongst other uses, this allows for better (fixed) documentation
regarding how many additional logging targets the user can define.

ClusterLabs/libqb,ClusterLabs/libqb,ClusterLabs/libqb,kgaillot/libqb,kgaillot/libqb,kgaillot/libqb