Minor code cleanup and improvements w.r.t. reductions
Minor code cleanup and improvements w.r.t. reductions

Continuing what Sung started yesterday, this commit cleans up some
more code around reductions that I noticed when we were examining
them:

- simplifies the computeDTF() logic a little bit, but also adds in
  local variables to avoid re-indexing an array (the Chapel
  compiler doesn't remove common subexpressions like this, so I'm
  doing it manually, essentially)

- gets rid of the courant_elem and dthydro_elem variables that were
  used in minloc reductions but then dropped on the floor.  After
  inspecting the MPI code, I believe that this was a side effect
  of writing global reductions by hand in MPI and not necessary in
  Chapel.

- rewrote the second minloc reduction as a simple min reduction,
  similar to what Sung did yesterday.

- moved the expression that calculates the HydroConstraint into 
  a helper function, similar to the CourantConstraint, mostly
  to clean up the code and do a similar CSE optimization as above.




git-svn-id: 88467cb1fb04b8a755be7e1ee1026be4190196ef@20767 3a8e244f-b0f2-452b-bcba-4c88e055c3ca

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