added proof-of-concept test/fvSolutionCombine

- could also move to utilities/miscellaneous

- the dictionary compare contents might be useful enough to move
  into dictionary code.

- usage example (w/o -rewrite):

      for i in $(find -name fvSolution)
      do
          fvSolutionCombine -case "${i%/system/fvSolution}"
      done