In the previsous commit the physics modifications between cy48t1 and cy48t3
have been introduced in PHYEX but still using the cy48t1 pack.
This commit introduces new modifications (in arome/ext) to use the cy48t3 pack.
Results are different due to modifications introduced betwwen cy48t1 and cy48t3
in parts other than the physics.
So, a new reference is needed (modifications in check_commit_ial.sh, INSTALL_pack_ial.md).

Original code contained a bug (autoconversion ri->rs was not set
to 0 if ldsoft when ri content gets lower than the threshold).
Introducing REPRO48 in ice4_slow allows to suppress the one
introduced in compute_pdf to compensate.

Suppression of ZMASK (DO with IF tests)
Arrays declared with KPROMA size

Suppression of ZMASK (DO with IF tests)
Arrays declared with KPROMA size

All modd_* replaceed by structures in ICE3

Modifications prepared by Ryad are stored in arome/modset_Ryad
To help the merging of ice4_fast_ri, the array syntax was replaced
by a DO loop