Hi all,
In order to purge the inbox, I've been in the process of reviewing
brainfuck code (a very slow process). While at it, I decided to
revisit the solution for nested exception handlers (see
testHandlerFromAction).

There are two similar and obsolete fixes in the inbox (due to
ContextPart->Context transition), Kernel-nice.857 and Kernel-fbs.870
(backported from Cuis) that I moved to treated inbox for that reason.
https://source.squeak.org/treated/Kernel-nice.857.diff
https://source.squeak.org/treated/Kernel-fbs.870.diff

Alas, those two solutions break the very peculiar expectations of
testHandlerReentrancy. This is a pity, because to my knowledge, those
expectations are essential for Tweak and Croquet.

There was a previous attempt from Andreas which was more a simple hack
in handleSignal:, that is to disable the handler by setting the temp
variable handlerActive in on:do: to false (self tempAt: 3 put: false).
I've generalized this solution.
https://source.squeak.org/treated/Kernel-ar.540.diff

However, there are several reasons why this does not work: the first
one, objected by Julian Fitzell here
http://lists.squeakfoundation.org/pipermail/squeak-dev/2011-January/156453.html
is that the handler must be able to handle a secondary exception
raised by the defaultAction. We can find similar expectations with
other exception handling, like resignalAs (I will publish another test
soon).

However, there is some simple strategy: before resuming the exception,
scan the context stack a second time so as to rearm the exception
handlers that we disabled during handleSignal:.

The major drawback, is that I have to spread a few self
reactivateHandlers here and there, virtually before every send of
#resumedUnchecked:.
The second drawback is that scanning the stack a second time is not
the most economical solution, but I don't care too much, we have to
make it right first.

If you find the courage to review, or more easily just to test it,
find it in the inbox...
Oups, I accidentally published in trunk...
Well the review will be forced, if you don't like it, admin please
remove or revert.
Sorry.