__WARN__ handler calls itself recursively

[karenetheridge]

I did use Devel::Confess twice in my codebase and ended up dying with: Deep recursion on subroutine "Devel::Confess::_warn" at .../IO/All.pm line 148. The warn handler is being overridden twice, resulting in a goto to ourselves -- if the warn handler is to be kept, a != check needs to be done first!

[wchristian]

Some discussion on that in #70

[karenetheridge]

I updated the title and description to match my actual problem, leaving the question of the handler's necessity to the other ticket.