Propagate plframe's db (double buffering configuration management) subcommand out to the megawidget's public interface.  Itk based apps can now easily configure double buffering on a plframe.
Propagate plframe's db (double buffering configuration management)
subcommand out to the megawidget's public interface.  Itk based apps
can now easily configure double buffering on a plframe.

svn path=/trunk/; revision=2068

FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot