SI-8024 Pending test case for package object / overloading bug

The error is new in 2.11, but actually seems correct. It appeared
in 2.11.0-M4, more specifically, after
https://github.com/scala/scala/pull/1554

But, the error message itself is wrong, and suggests that a method
symbol has latched itself to an incorrect owner.
SI-8024 Fix inaccurate message on overloaded ambiguous ident

`Symbol#owner` of an overloaded symbol doesn't necessarily correspond
to the owner of any of the alternatives, and as such it shouldn't
be used in error message.

neg/t8024.scala actually represents a progression since 2.10.3;
the ambiguity was not reported. I bisected the change to
https://github.com/scala/scala/pull/1554.
SI-8024 Improve user-level toString of package objects

We were outputing a the unattractive `package package`;
now we opt for `package object pack`.

Under `-Ydebug`, we still go to the "accurate" mode of the
old `toString` implementation, which differentiates package objects
vs package object classes.