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)
 ##{

moo/kernel/generr.moo

@@ -77,9 +77,8 @@ class MyObject(Object)
 			'duplicate class'
 			'contradictory class definition'
 			'wrong class name'
-			'non-pointer class not allowed to inherit a superclass with trailer size set'
-			'not allowed to inherit a #final class'
-			'invalid class type size'
+			'invalid non-pointer instance size'
+			'prohibited inheritance'
 			'variable declaration not allowed'
 			'modifier expected'
 			'wrong modifier'