javac should be updated to conform to Lambda Spec bug fix JDK-8029306.

The spec failed to account for the possibility that the qualifying type of an unbound method reference might be a wildcard-parameterized type.

The fix is to perform capture conversion on this type (as well as the type that is inferred to fill in type arguments for a raw type).

The following should compile without error:
  Function<Optional<?>, Object> f1 = Optional<?>::get;
  Function<Optional<Integer>, Number> f2 = Optional<? extends Number>::get;
  Function<LinkedList<? extends Integer>, Integer> f3 = Queue::peek;

Current errors (tested b115):

error: incompatible types: invalid method reference
  Function<Optional<?>, Object> f1 = Optional<?>::get;
                                     ^
    method get in class Optional<T> cannot be applied to given types
      required: no arguments
      found: Optional<?>
      reason: actual and formal argument lists differ in length
  where T is a type-variable:
    T extends Object declared in class Optional

error: incompatible types: invalid method reference
  Function<Optional<Integer>, Number> f2 = Optional<? extends Number>::get;
                                           ^
    method get in class Optional<T> cannot be applied to given types
      required: no arguments
      found: Optional<Integer>
      reason: actual and formal argument lists differ in length
  where T is a type-variable:
    T extends Object declared in class Optional

AbstractCRef.java:7: error: incompatible types: bad return type in method reference
  Function<LinkedList<? extends Integer>, Integer> f3 = Queue::peek;
                                                        ^
    ? extends Integer cannot be converted to Integer