code generation fails for tuples as the result of a branch operation

[tmcdonell]

For example:

permute const zeros (\ix -> ix `mod` 2 ==* 0 ? (ignore, tuple (ix,ix))) ones

*** Exception: Pattern match failure in do expression at Data/Array/Accelerate/CUDA/CodeGen.hs:137:2-4

[tmcdonell]

Fri Sep  3 09:43:24 EST 2010  Trevor L. McDonell <tmcdonell@cse.unsw.edu.au>
  * fix code generation for tuples as the result of a branch

Pushes the conditional into each tuple component. Not optimal code (unless nvcc is clever enough to only evaluate the conditional once) but should work for now.