[MITgcm-support] Changes in pickup files

[Jean-Michel Campin]

Hello MITgcm users,

Today, I changed the way the model read and write pickup files,
(code newer than checkpoint59i) for the restart process.
For now, it only affects the main pickup files (pickup written by
packages will follow) and non-netcdf pickup (not MNC).

The model is now reading the "pickup.[].meta" file associated with
the binary file(s) "pickup.[].data", and figures out if it can restart
correctly.
In case of a missing filed, it will stop (if pickupStrictlyMatch=T, =
the default) or try to restart (if pickupStrictlyMatch=F), even if the
restart is not perfect (i.e., no zero diff compared no stop-restart).

The main advantages are:
 - more flexible (adding/removing fields in the code is much more easy).
 - safer (check for missing fields).
 - save some disk space (since it only writes fields which are needed)

The changes are fully backward compatible, and the new code can still
restart from old pickup files (produced with an older version of the
code, until checkpoint59i ), with:
 1) the corresponding meta files, and
 2) adding " pickupStrictlyMatch=.FALSE.," in 3rd namelist: "PARM03"
    of parameter file "data".
If you did not keep any meta file (which is not recommended anymore),
 MITgcm/verification/global_ocean.90x40x15/input/pickup.0000036000.meta
is the minimal meta file which is recognized as "old-pickup" format.

If something does not work as it should, please report to the list.
This will help to get rid of platform/compiler dependent problems
that might still be there (since the new pieces are IO related,
hard to check all the possibilities).

Jean-Michel