autogen.sh error on no warnings

[Norbert Thiebaud]

On Fri, Aug 24, 2012 at 9:02 AM, Ruslan Kabatsayev
<b7.10110111 at gmail.com> wrote:
> Hi Norbert,
>
> Your fix is not solving all the problem: now autogen fails without
> indication why. See the message:
>
>>If you want to run the smoketest, issue:
>>make check
>>
>>Error running configure at ./autogen.sh line 187.
> This is because you redirect error to /dev/null, but don't prevent cat
> error status. So this is better to be fixed either by first checking
> presence of warn ("[ -e warn ] && cat warn"), or adding "|| true" to
> "cat warn 2>/dev/null"

Sorry about that...

I restored the 'initialization of 'warn' since not only it need to
exist but also old content need to be discarded
otherwise a run _with_warning_ followed by a run without would still
print the previous run warning

Norbert