Update Hypre & Trilinos parallel solution to mimic internal parallel iterative solver
such that the partitionwise RHS vector is updated to include interface summing after
returning from ParallelIter(), in order for the ComputeChange() 'residual' mode to work
asis also with Hypre & Trilinos. A more consistent solution would have been to not
to change the RHS within ParallelIter() even when doing ElmerSolver internal
iterative methods, but afraid that this might break some unexpected code paths... 


git-svn-id: svn://svn.code.sf.net/p/elmerfem/code/trunk@6922 04224531-1f84-46d8-96ce-875b9e37dce3