Someone pointed out in a bug report (#1436) that if you create a
too-long cluster name, there are objects that contain cluster name +
other characters, meaning that the maximum size is lower than the max
size of namespace names.

I think the max column size is 64, right?  If that be the case, then the
fact that generated columns are of the format
_Slony-I_[CLUSTER_NAME]_rowID means that we have to step back by 15
characters, to 49.

I'm game on having slonik reject cluster names that are of excessive
length...  Has anyone noticed other generated names that might restrict
size further?

I'll see about setting a 49 char restriction, and documenting it; if we
have to go further, that provides a natural place to document further...