Tref and Sref used in simplified eos hard coded

[mathiot]

Context

The simplified eos (ln_seos) is based on :

rd(T,S,Z)*rho0 = -a0*(1+.5*lambda*dT+mu*Z+nu*dS)*dT+b0*dS

It need a reference T and S hard coded into eosbn2 (respectively, 10 and 35) to compute dt and ds. All the other coefficients (thermal expension, cabbeling and thermobaric) are defined in the namelist.

Recommendation

Add the definition of the reference T and S used in the simplified eos in the namelist (default being the current value).

Other benefits:

• more flexibility of the seos.
• no more eosbn2.F90 in ISOMIP+/MY_SRC (see #2536)