Fix dangling reference in weak ref code.

Another test added as a result of coverage analysis.

Test/ARCTest_arc.m

@@ -0,0 +1,35 @@
+#import "Test.h"
+
+id __weak var;
+
+@interface ARC : Test @end
+@implementation ARC
+- (id)loadWeak
+{
+	return var;
+}
+- (void)setWeakFromWeak: (id __weak)anObject
+{
+	var = anObject;
+}
+- (void)setWeak: (id)anObject
+{
+	var = anObject;
+}
+@end
+
+
+int main(void)
+{
+	ARC *obj = [ARC new];
+	{
+		id o1 = [Test new];
+		id o2 = [Test new];
+		[obj setWeak: o1];
+		assert([obj loadWeak] == o1);
+		[obj setWeakFromWeak: o2];
+		assert([obj loadWeak] == o2);
+	}
+	assert([obj loadWeak] == nil);
+	return 0;
+}

Test/CMakeLists.txt

@@ -7,6 +7,7 @@
 set(TESTS
 	alignTest.m
 	AllocatePair.m
+	ARCTest_arc.m
 	AssociatedObject.m
 	AssociatedObject2.m
 	BlockImpTest.m

arc.m

@@ -671,6 +671,7 @@ static inline BOOL weakRefRelease(WeakRef *ref)
 	ref->weak_count--;
 	if (ref->weak_count == 0)
 	{
+		weak_ref_remove(weakRefs, ref->obj);
 		free(ref);
 		return YES;
 	}