[UPDATE][NEW] BooleanHandler; wrap request info type

type BooleanHandler: Handler for boolean type (actually just an integer, but
	application code thinks it's setting a boolean).

type RequestInfo: A type wrapping the CGO type. This should be a Go type
	with the fields copied, but for the timebeing it lets client code
	avoid cgo.

OIDHandler callbacks now take both a RequestInfo object and the OID.

Some DRY with scalar registration.