swift234

Use TupleShuffleExpr to finally eliminate the last remenants of the 
ASDAG.  Our AST is actually a tree again.  The testcase compiles into:
...
          (vardecl 'c' type='(a : int, b : int)')
          (vardecl 'd' type='(b : int, a : int)'
            (tuple_shuffle type='(b : int, a : int)' Elements=[1, 0]
              (declref_expr type='(a : int, b : int)' decl=c))))))



Swift SVN r387