faster proc generic for obtaining real lambdas from function objects
faster proc generic for obtaining real lambdas from function objects

still not sure why (and if always) implementing default method within
generic definition is much faster then implementation of unspecialized
method

akapav/js,marijnh/js,jimiejosh/js,jimiejosh/js,akapav/js,marijnh/js,jimiejosh/js,marijnh/js,akapav/js