Allow zero width replications only in a concatenation.

1364-2001 does not allow a replication count of zero, but
1364-2005 allows them when the replication is enclosed in
a concatenation with other valid bits. This patch adds
code to perform these checks for procedural expressions.
Because of the NetNet object must have a width greater
than zero a replication used in a continuous assignment
can never have a count of zero.

elab_net.cc

@@ -1591,7 +1591,7 @@ NetNet* PEConcat::elaborate_net(Design*des, NetScope*scope,
 
 	    if (repeat == 0) {
 		  cerr << get_fileline() << ": error: Concatenation repeat "
-			"may not be 0."
+			"may not be zero."
 		       << endl;
 		  des->errors += 1;
 		  return 0;
@@ -1689,7 +1689,6 @@ NetNet* PEConcat::elaborate_net(Design*des, NetScope*scope,
 	    }
       }
 
-
       osig->local_flag(true);
       return osig;
 }