Change reference version for NEC
Use of sendmail for aurora01

S. Riette 12 Dec 2023: call nucleation from a loop to have bit-reproducibility on NEC by changing number of threads

Architecture files can be created in $HOME/.phyex/fcm_arch
The PYFT_OPTS variable can be put in the architecture env file to add pyft transformations

Last part of #17

Use of DIFF in rain_ice_old testprog
Remove useless dimension in other testprogs

Another part of #17

Part of #17

Due to the switch between filepp/mnh_expand and pyft_tool.py,
old commits cannot be compiled with the tools provided by recent commits

This reverts commit 21056271.