optimize fusion, reduce memory used of fusion (from iTask branch):
allow integers and strings as consumer for generic functions (to optimize use of generic info). use PR_CurriedFunction instead of PR_Curried for local macro functions that are good producers. check the arity of the function to be generated already in determineProducer, if too large, don't yield a producer which will be rejected later, to allow optimization of producers in subsequent arguments. optimize trivial function calls (with arguments) before optimizing arguments, treat constant function as trivial function. if a function call has two identical arguments, generate a specialized function that shares these parameters. specialize functions with zero arity constructor arguments, if the function is a generic function, or the constructor is a generic constructor.