Removing the temperature of the triple point of water from the code

[barthele]

273.16 is the temperature of the triple point of water in K (​http://en.wikipedia.org/wiki/Triple_point).

It has nothing to do with conversions between K and °C (+/- 273.15). Also, it is not the melting point of fresh water (273.15 K).

Hence, neither the "temperature of the triple point of water" nor the value "273.16" have reasons to appear in an ocean or sea ice code.

In phycst.F90, we should:

• suppress the variable rtt (= 273.16, "triple point of temperature"), and replace all its occurences in the code by the already existing rt0 (= 273.15, "freezing point of fresh water");

• change the values of the variable rt0_snow and rt0_ice ("melting point of snow/ice") in case LIM3 is used from 273.16 to 273.15.

I have tested this for 10 years, ORCA1, CLIO forcing formulation, LIM3. The changes in the results are negligible.

[vancop]

Done in revision 5138