Important: Corrected bug in obs_write,F when using BGQC

[arango]

• A bug was corrected in routine obs_write.F to remove global reduction operation for BgThresh. The following statement:

            CALL mp_collect (ng, model, Ncollect, IniVal,                 &
  #    if defined WEAK_CONSTRAINT
       &                     BgThresh(Mstr:))
  #    else
       &                     BgThresh)
  #    endif
  

  is not needed since BgRhresh does no depend on tile partition. Actually, if we make this call its final values are target values times the number of MPI node used because of reduction summation.

• I also fixed a typo in tl_pre_step3d.F and rp_pre_step3d.F in the commented nonlinear code.

• Added date string reporting in routines obs_read.F and ad_htobs.F.