Changes

This commit fixes 2 issues in regards to hydrometeor sedimentation:

1) The code was taking into consideration the value of the hydrometeor
   at the ghost point within the center-differenced option.
2) If a hydrometeor was present (value > 0) at the highest thermodynamic grid level, the code was potentially not conservative.

Both these issues are fixed with this commit. The results are
BIT_CHANGING.