enhanced set_syntax_errbmsg() to set_syntax_errbfmt().

collapsed three separate syntax error code to a single code MOO_SYNERR_INHERITBANNED.
added moo_seterrbfmtv() and moo_seterrufmtv() for internal use

moo/kernel/Socket.moo

@@ -234,6 +234,9 @@ class X(Object)
 class(#byte(3)) Y(X)
 {
 }
+class (#word(2)) Z(Y)
+{
+}
 
 ##class InetSocketAddress(SocketAddress)
 ##{