WRF model_mod - Why not allow last level?

Problem

My WRF simulation has 50 levels, (51 staggered) but debugging the obs_def_rttov_mod.f90 showed that it sees 49 levels and 48 layers. (see image here)

Reason

rttov_mod.f90 determines the number of levels in the COUNTLEVELS loop (https://github.com/NCAR/DART/blob/9c7d829a507311625edcaf0c145a580811fcd513/observations/forward_operators/obs_def_rttov_mod.f90#L3526)
and this loop stops at level 49 (wrong) since interpolate returns istatus 99
This is because interpolate checks the bounds and does NOT allow to retrieve the value at the last level (https://github.com/NCAR/DART/blob/9c7d829a507311625edcaf0c145a580811fcd513/models/wrf/model_mod.f90#L2042)

Solution

So I propose to change the code so that it also allows to access the last level (https://github.com/NCAR/DART/commit/25efb6c8ac49e5322300e0a5dd2244dc61e157bb)

This change will be part of the https://github.com/lkugler/DART/tree/rttov13 push request

Read the COUNTLEVELS loop in observations/forward_operators/obs_def_rttov_mod.f90 and the bounds check in models/wrf/model_mod.f90. Compare the behavior with the proposed commit and verify that the WRF simulation exposes the expected final level rather than returning status 99; the issue is resolved when the level and layer counts include the last level.