Report dangerous callin bindings (equals & hashCode)

[stephan]

When callin-binding a base class's equals or hashCode method, a StackOverflowError can occur because the lifting infrastructure uses exactly these methods during callin dispatch.

I recently (r19249) ensured that isExecutingCallin() is checked early enough so that the following binding works:

myEquals <- replace equals
  base when (!isExecutingCallin());

(See also 9.2.4-otjld-is-executing-callin-called-5, note that the role cache has to be filled with lots of roles for a hash-conflict to occur so that equals() will actually be called).

However, calling bindings to these two methods should be flagged with a warning to alert the user of the danger of infinite recursion.

[stephan]

New tests in 4.1.41-otjld-dangerous-callin-binding-1, 4.1.41-otjld-dangerous-callin-binding-2, 4.1.41-otjld-dangerous-callin-binding-3

Implementation in r19308.

[stephan]

Test pass, no regression, closing as fixed.