[Dart-users] added relative humidity forward operator

[Nancy Collins]

hi dart-users,

i've just committed a new relative humidity forward operator
contributed by ryan torn.  the previous definition of a relative
humidity observation called directly into a model interpolate
routine and would have failed if the model state vector didn't
contain a relative humidity field.  the new forward operator
requires the model be able to interpolate temperature,
pressure, and a vapor mixing ratio in order to compute the value.

the update includes updated preprocess namelists to add
the obs_def_rel_humidity_mod.f90 to the list of observation
modules compiled into the models and observation converters
that use it.

this change is on the head of the subversion trunk.   there were
no changes to either dewpoint or specific humidity observations
or forward operators.

if you have any questions, please email:  dart (at) ucar.edu

thanks,
nancy