[suzerain]: for #2995, converting all MPI_Reduce to AllReduce, in hopes this is causing older MPI stack failures due to unsupported in-place reduces. 




git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@42551 0bd85f0b-c151-43b9-a1e9-27231104551f
suzerain: #2995 simplify/broaden Reduce fix r42551

Since we're paying to Allreduce instead of Reduce,
might as well have all ranks contain correct information
at the end of the routine.  Also happens to simplify
the logic considerably.  Method doxygen updated to reflect
new parallel semantics.

Repeats fix for #2995 erroring out on Cab under apps/perfect
in both quantities.{cpp,hpp}.

Remaining MPI_Reduce calls throughout the library appear to
not employ MPI_IN_PLACE in this manner.
and layers.{cpp,hpp}.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@42554 0bd85f0b-c151-43b9-a1e9-27231104551f