Fiduccia Mattheyse doesn't support partitioning into more than two parts

[msalib]

The docs for FM say:

This implementation is an extension of the original algorithm to handle partitioning into more than two parts.

But if you set any value of the partition vector to a value greater than one, you'll get a BiPartitioningOnly error.

[hhirtz]

Good catch! Thanks for the report. coupe could implement extensions for FM but in the meantime I'll update the docs.