use the ""filter iteration count"" on a wider scale, down to matrices
Imported issue: Initially reported by @thome in https://gforge.inria.fr/tracker/?group_id=2065&aid=20664
purge may run several times in the normal course of a computation. Or we may want to interrupt it and start over. This will bump the iteration count in the purge.stdout files.
I suggest this iteration count be used as well in the merge stdout and stderr files, ditto for replay, and that the matrices we output are also numbered the same way. This also includes the directory name for bwc, and the name of the sm file.
This would allow one to unambiguously link this stdout file to this matrix, and this working directory.
It takes some hacking in the python code...