Modifications from Aladin

Contains:

• extraction of the Cd drag coefficient from SURFEX to be added in the interface of ARO_GROUND_DIAG.
  Only 3 SURFEX routines are concerned.
  The aim is to improve the interface with ALARO.

This contribution is ready and was tested in operational mode with ALARO+SURFEX.

R. Hamdi will put in into SURFEX V8.

These light modifications will probably be included among the last intermediate ones.

As this contribution concerned only 2 SURFEX files, it was included in branch NEW_PREP December,6th 2013.