Tweaking the code sample for 'A Case of Equality'

[demobox]

• removing the 'regular' classes since they result of their comparisons is too easy to get right
• adding a different case class definition that also uses the "problematic" base trait but does not affect case class comparison

Came across this while fixing the code sample to work with 2.11. I think the result is pretty puzzling, to be honest:

scala> println(cc1 == cc2)
In equals
true

scala> println(cc1.## == cc2.##)
true

scala> println(ccd1 == ccd2)
In equals
false

scala> println(ccd1.## == ccd2.##)
true

[demobox]

@nermin @dgruntz: Comments, thoughts, suggestions welcome!

[demobox]

PS: Please do not merge yet - will squash'n'rebase first.

[nermin]

Wish I saw this one earlier, since I already reviewed the puzzler and liked quite a lot the improvement, I see no problem with merging it.