Annotate reduction parallel loops in the IslAst textual output

  + Introduced dependency type TYPE_TC_RED to represent the transitive closure
    (& the reverse) of reduction dependences. These are used when we check for
    reduction parallel loops.
  + Test cases including loop reversals and modulo schedules which compute
    reductions in a alternated order.


git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@213019 91177308-0d34-0410-b5e6-96231b3b80d8