Change upvalues to point to the LuaState instead of directly to the stack.

This change has two benefits:
 * Reference to LuaState's stack does not need to be adjusted when
   the stack needs to grow.
 * One less heap object for a closed upvalue.

src/core/org/luaj/vm/LuaState.java

@@ -875,14 +875,14 @@ public class LuaState extends Lua {
         int i;
         for ( i = this.upvals.size() - 1; i >= 0; --i ) {
             up = (UpVal) this.upvals.elementAt( i );
-            if ( up.stack == this.stack && up.position == target ) {
+            if ( up.state == this && up.position == target ) {
                 return up;
             } else if ( up.position < target ) {
                 break;
             }
         }
         
-        up = new UpVal( upValName, this.stack, target );
+        up = new UpVal( upValName, this, target );
         this.upvals.insertElementAt( up, i + 1 );
         return up;
     }

src/core/org/luaj/vm/UpVal.java

@@ -25,12 +25,13 @@ package org.luaj.vm;
 public class UpVal {
 
 	private LString name;
-	public LValue[] stack;
-	public int position;
+	LuaState state;
+	int position;
+	LValue value;
 	
-	public UpVal( LString string, LValue[] stack, int i ) {
+	public UpVal( LString string, LuaState state, int i ) {
 		this.name = string;
-		this.stack = stack;
+		this.state = state;
 		this.position = i;
 	}
 	
@@ -39,18 +40,23 @@ public class UpVal {
 	}
 	
 	public LValue getValue() {
-		return stack[ position ];
+		if ( state == null )
+			return value;
+		else
+			return state.stack[ position ];
 	}
 	
 	public void setValue( LValue value ) {
-		stack[ position ] = value;
+		if ( state == null )
+			this.value = value;
+		else
+			state.stack[ position ] = value;
 	}
 	
 	public boolean close( int limit ) {
 		if ( position >= limit ) {
-			final LValue v = stack[ position ];
-			stack = new LValue[] { v };
-			position = 0;
+			value = state.stack[ position ];
+			state = null;
 			return true;
 		} else {
 			return false;