Add c-type variants for .bool_set_(inverse):N key properties

All other variable types already have c-type variants available: for
consistency.

As it's not easy to generate key property variants, other similar check-ins
are coming up!


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4507 de43f980-851b-0410-b2f7-c40aca1f87e0