Improve weak table implementation

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

@@ -30,7 +30,7 @@ public class LuaTable extends LuaValue {
 	protected LuaValue[] array;
 	protected LuaValue[] hashKeys;
 	protected LuaValue[] hashValues;
-	private int hashEntries;
+	protected int hashEntries;
 	protected LuaValue m_metatable;
 	
 	public LuaTable() {
@@ -170,7 +170,7 @@ public class LuaTable extends LuaValue {
 		return hashget( key );
 	}
 		
-	private LuaValue hashget(LuaValue key) {
+	protected LuaValue hashget(LuaValue key) {
 		if ( hashEntries > 0 ) {
 			LuaValue v = hashValues[hashFindSlot(key)];
 			return v!=null? v: NIL;

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

@@ -317,8 +317,9 @@ public class LuaValue extends Varargs {
 	
 	// lua number/string conversion
 	public LuaString strvalue()     { typerror("strValue"); return null; }
-	public LuaValue  strongkey()    { return this; }
+	public LuaValue  strongkey()    { return strongvalue(); }
 	public LuaValue  strongvalue()  { return this; }
+	public boolean   isweaknil()    { return false; }
 
 	// conversion from java values
 	public static LuaBoolean  valueOf(boolean b)    { return b? LuaValue.TRUE: FALSE; };

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

@@ -269,7 +269,6 @@ public class WeakTable extends LuaTable {
 			this.weakvalue = weakvalue;
 		}
 
-		// when looking up the value, look in the keys metatable
 		public LuaValue strongvalue() {
 			LuaValue key = weakkey.strongkey();
 			if ( key.isnil() )