document idemix related changes in ggl90:   - re-organize code in s/r ggl90_calc a little to move computations that     are different for idemix into separate loops (changes verification     experiements at truncation level)   - requires 2 new 2D fields KappaM, verticalShear   - make hFacI and recip_hFacI local 3D variables that are passed to     s/r ggl90_idemix   - fix and improve some comments
document idemix related changes in ggl90:
  - re-organize code in s/r ggl90_calc a little to move computations that
    are different for idemix into separate loops (changes verification
    experiements at truncation level)
  - requires 2 new 2D fields KappaM, verticalShear
  - make hFacI and recip_hFacI local 3D variables that are passed to
    s/r ggl90_idemix
  - fix and improve some comments

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