Fix error messages for pass tests.

src/core/org/luaj/vm2/LuaValue.java

@@ -21,8 +21,6 @@
 ******************************************************************************/
 package org.luaj.vm2;
 
-import org.luaj.vm2.Varargs;
-
 /**
  * Base class for all concrete lua type values.
  * <p>
@@ -3362,7 +3360,7 @@ public class LuaValue extends Varargs {
 	protected LuaValue checkmetatag(LuaValue tag, String reason) {
 		LuaValue h = this.metatag(tag);
 		if ( h.isnil() )
-			throw new LuaError(reason+typename());
+			throw new LuaError(reason + "a " + typename() + " value");
 		return h;
 	}