Double-checked locking fixed in LockBasedStorageManager

There were two problems here:
 * a volatile field was read and then a local variable used, i.e. the field might have been changed in between the check and the return;
 * this volatile read was unnecessary, because the whole purpose of `_value` local variable is to avoid it.

core/util.runtime/src/org/jetbrains/jet/storage/LockBasedStorageManager.java

@@ -277,7 +277,7 @@ public class LockBasedStorageManager implements StorageManager {
         @Override
         public T invoke() {
             Object _value = value;
-            if (!(value instanceof NotValue)) return WrappedValues.unescapeThrowable(_value);
+            if (!(_value instanceof NotValue)) return WrappedValues.unescapeThrowable(_value);
 
             lock.lock();
             try {