Generalize d-p to work with any label provided by d-static.

d-p is generalized so each node can handle the usual string labels
and some other type of labels specified by the user. newLocalNode
now has an additional parameter to specify the type of labels.

When using spawn and friends, the labels of Closures and Static values
must be of the user-specified type on the remote side, otherwise a
runtime error ensues.

As a side-effect of the generalization, the combinators defined in
C.D.P.Internal.Closure.BuiltIn have been removed from the public
interface of d-p. The generalized combinators are cumbersome to use
for the user. Specialized versions of these combinators should work
better and there is no particular reason to place them in d-p.