…ncy than coupling

Mostly changes comments and documentation

Also removes a trailing comma from a list in python

I'm not sure this is necessary, but it seems safest

Mariana had changed this to use glcrun_avg_alarm. But I think this work
should really be done every time glc is run, even if it's not an
averaging time.

If specifying GLC_AVG_PERIOD = 'glc_coupling_period', we'll
automatically set the averaging clock to match the glc run clock. This
provides more robustness than the earlier hard-coded 'daily' option, in
case the glc coupling period is not actually daily.

Abort if it's ever the case that glcrun_avg_alarm is true, but
glcrun_alarm is false

In principle we shouldn't need to zero the fields at these times -
instead, glc should just ignore the fields at these times. However, some
tests (like an ERS or ERI test that stops the final run segment
mid-year) can fail if we don't explicitly zero the fields, because the
x2g fields can then differ upon restart.

The refactored logic in cesm_comp_mod also results in these changes:

(1) This code:

         !----------------------------------------------------
         !| cpl -> glc
         !----------------------------------------------------

         if (iamin_CPLALLGLCID .and. glc_prognostic) then
            call component_exch(glc, flow='x2c', &
                 infodata=infodata, infodata_string='cpl2glc_run', &
                 mpicom_barrier=mpicom_CPLALLGLCID, run_barriers=run_barriers, &
                 timer_barrier='CPL:C2G_BARRIER', timer_comp_exch='CPL:C2G', &
                 timer_map_exch='CPL:c2g_glcx2glcg', timer_infodata_exch='CPL:c2g_infoexch')
         endif

will now only be executed if glcrun_alarm is true. That's what happened
on master, but the previous version of the branch executed it even if
glcrun_alarm was false.

(2) This code:

                  call cesm_comp_barriers(mpicom=mpicom_CPLID, timer='CPL:GLCPREP_BARRIER')
                  call t_drvstartf ('CPL:GLCPREP',cplrun=.true.,barrier=mpicom_CPLID)
                  if (drv_threading) call seq_comm_setnthreads(nthreads_CPLID)

and then:

                  if (drv_threading) call seq_comm_setnthreads(nthreads_GLOID)
                  call t_drvstopf  ('CPL:GLCPREP',cplrun=.true.)

will happen even if .not. glcrun_avg_alarm

…with CISM

This used to be used by CLM, but is no longer needed.