SI-9365 Don't null out dependencies of transient lazy vals

As per Iulian's analysis:

> When lazy vals are transient, the optimization in SI-720 is invalid,
> leading to NPEs.

These NPEs appear when recomputing the lazy val when deserializaing
the object.

This commit disables the field nulling if the lazy val is marked
transient.

The post-mixin tree in the enclosed test changes as follows:

```
--- sandbox/old.log	2015-07-27 15:48:03.000000000 +1000
+++ sandbox/new.log	2015-07-27 15:47:56.000000000 +1000
@@ -1,61 +1,54 @@
 [[syntax trees at end of                     mixin]] // t9365.scala
 package <empty> {
   class Test extends Object with Serializable {
     @transient @volatile private[this] var bitmap$trans$0: Boolean = false;
     private def foo$lzycompute(): Object = {
       {
         Test.this.synchronized({
           if (Test.this.bitmap$trans$0.unary_!())
             {
               Test.this.foo = Test.this.x.apply();
               Test.this.bitmap$trans$0 = true;
               ()
             };
           scala.runtime.BoxedUnit.UNIT
         });
-        Test.this.x = null
+        ()
       };
       Test.this.foo
     };
```

In addition to the test from the ticket, I've added a reflection
based test that directly tests the nulling. This complements the
test added in 449f2a7473, the fix for SI-720, which passes by
virtue of not exhausting the heap.

1 files changed, 18 insertions, 0 deletions

diff --git a/test/files/run/t9365.scala b/test/files/run/t9365.scala
new file mode 100644
index 0000000000..0c4477dda9
--- /dev/null
+++ b/test/files/run/t9365.scala
@@ -0,0 +1,18 @@
+class Test(x: => Object) extends Serializable {
+  @transient lazy val foo = x
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    import java.io._
+    val t = new Test("foo")
+    println(t.foo)
+    val baos = new ByteArrayOutputStream
+    val dos = new ObjectOutputStream(baos)
+    dos.writeObject(t)
+    dos.close()
+    val dis = new ObjectInputStream(new ByteArrayInputStream(baos.toByteArray()))
+    val t1 = dis.readObject().asInstanceOf[Test]
+    println(t1.foo) // was NPE
+  }
+}