Make DOCBOOK_XML_BACKEND ON mandatory rather than an option. This change effectively disables the old SGML/DSSSL backend tools that were deprecated but still available for 5.9.10 and which were the default for releases prior to 5.9.10.
Make DOCBOOK_XML_BACKEND ON mandatory rather than an option.
This change effectively disables the old SGML/DSSSL backend tools that
were deprecated but still available for 5.9.10 and which were the
default for releases prior to 5.9.10.


svn path=/trunk/; revision=12581

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