fixed warnings

from the author of Devel::TrackObjects

Hi, 

$tracked->[0] is the object itself.

If you print it it will stringify it. Stringification is overloaded
in Date::Time using Date::Time::_stringify, which will use ymd and hms
to stringify the object.

If the Date::Time object itself contains no $self->{local_c} yet the
values for sprintf in ymd and hms will be undef which causes the 
warnings.

So this is not really a bug in DateTime, because they never intended
for somebody to stringify some internal objects. But it's not a bug
in Devel::TrackObjects either.
Let's just say, they are not made to work close together.

But I've worked now around this overloading when debugging is enabled
(just released 0.5, see https://github.com/noxxi/p5-devel-trackobjects)
and so can you: 

    + use overload;
    ...
    -      warn $tracked->[0];
    +      warn overload::StrVal($tracked->[0]);


Regards,
Steffen