Allow use_init_interp in a branch case even though it doesn't do anything

[billsacks]

If you try to run a branch case with use_init_interp = .true., the model dies at runtime with the message, ERROR: Can only set use_init_interp if finidat is set.

On the surface, this check that use_init_interp can only be set if finidat is set seems reasonable. However, it causes problems in practice if you set up a branch case using a compset and resolution for which use_init_interp are set automatically (via CLM_NAMELIST_OPTS) (note that that automatic setting is done in some CESM2.1 release configurations in order to have some compset/resolution combinations automatically give a hybrid case with use_init_interp = .true., to interpolate from the out-of-the-box refcase). This was a problem in the recent CESM tutorial.

We should reduce the error checking on use_init_interp, so that it can be set to .true. even if finidat is not set. In this case, it should just be ignored, and a warning message should be printed to the log file stating that we're ignoring use_init_interp in this branch run.

I reproduced this on my mac as follows:

First, I created a startup case:

./create_newcase --case /Users/sacks/projects/scratch/check_branch_baseline_0813a --compset I2000Clm50BgcCropQianRsGs --res f10_f10_musgs --run-unsupported

./xmlchange NTASKS=4
./xmlchange STOP_N=1

Then I created a branch:

./create_newcase --case /Users/sacks/projects/scratch/check_branch_0813a --compset I2000Clm50BgcCropQianRsGs --res f10_f10_musgs --run-unsupported

./xmlchange NTASKS=4
./xmlchange RUN_TYPE=branch
./xmlchange RUN_REFCASE=check_branch_baseline_0813a
./xmlchange RUN_REFDATE=2000-01-02
./xmlchange STOP_N=1
./xmlchange GET_REFCASE=FALSE
./xmlchange CLM_NAMELIST_OPTS=use_init_interp=.true.

And I prestaged the restart files from the first case into the second case's run directory.

[ekluzek]

Fixed in release-clm5.0.28