Ok, no reaction for ~2 months, I decided to take a look at it on my own to get 
rid of this release-stopper.

Solution: I'll remove devscripts from grml's pool. It's *strongly* outdated, 
i386-only and unmaintained in our pool. The only reason why devscripts is in 
our repository at all is issue15:

./debchange.pl:    unless ($opt_D =~ /^(unstable|(stable|testing)(-security)?|
oldstable-security|experimental|grml-testing|UNRELEASED)$/) {
./debchange.pl: warn "$progname warning: Recognised distributions are: 
unstable, testing, stable,\nexperimental,grml-testing,UNRELEASED and 
{testing,stable,oldstable}-security.\nUsing your one anyway.\n";
./debian/changelog:devscripts (2.9.27.grml.1) grml-testing; urgency=low
./debian/changelog:  * Add grml-testing to dch (Closes: issue15)

But we don't use 'grml-testing' as release target in our changelogs nowadays. 
If we reconsider using grml-testing in the changelogs we should bug upstream of 
devscripts whether the accepted releases could be made configurable without 
touching the source.

regards,
-mika-