Bug 885798 - Extend the nc_slots enum with new Number constants. r=till

Follow-up to the previously-landed patch.

The lack of this extension happens not to matter because the
NC_EPSILON and NC_LIMIT enum values happen to not be used
in the file currently.

--HG--
extra : rebase_source : 4c6da4d6da68e133cc6799250f4bee4b92ed188f