octave-3.0: plotting delayed while prompted by 'keyboard'

[Olaf Till]

Octave version: Debians 'testing' octave3.0 source package compiled in
 Debian 'stable', ignoring build-dependencies

Problem: While in 'keyboard' debug modus, no plotting (with the usual
Gnuplot backend) is possible, neither from 'keyboard's prompt nor from
the script just before the 'keyboard' command. Can be reproduced by
typing 'keyboard' in a freshly started Octave and trying to plot
something with 'plot'. The plot figure appears on screen after leaving
the debug modus.

Sorry if this should have been reported before.

Olaf