Optionally removing replica suffix

[GiovanniBussi]

Since GROMACS 2019 the option -multi is gone, and one is forced to use -multidir. This makes the whole replica suffix stuff largely useless. I would not remove it (since other codes might still allow to run multiple replicas in the same dir), but I was wondering if we should give an option to disable it or even customize it. Something like

PRINT ARG=x FILE=colvar.dat # files are colvar.0.dat, colvar.1.dat, and colvar.2.dat, this will be the default
REPLICA_SUFFIX NONE
PRINT ARG=x FILE=colvar.dat # single file, should only be used with -multidir
REPLICA_SUFFIX CUSTOM=@replicas:A,B,C
PRINT ARG=x FILE=colvar.dat # files are colvarA.dat, colvarB.dat, and colvarC.dat
REPLICA_SUFFIX INDEX
PRINT ARG=x FILE=colvar.dat # files are colvar.0.dat, colvar.1.dat, and colvar.2.dat, restored the default

[valsson]

Sound like a good idea to me. I support keeping colvar.[replica#].dat as the default due to other codes such as LAMMPS (my group often uses the multiple walkers/replicas in LAMMPS). But having the option to disable the suffix or customize it would be useful.

[invemichele]

+1 for the option to remove the replica suffix