doc: Create new Graphic Properties Index (bug #52812). * doc/interpreter/pr-idx.txi: New index file. * doc/interpreter/module.mk: Add pr-idx.txi to build system. * genpropdoc.m: Place graphic properties in to @prindex. * octave.texi: Use "@defindex pr" to create a new index. Add "Graphics Properties Index" to menu. "@include pr-idx.texi" as last index after Operators Index. * plot.txi: Put "ObjectXXX Properties" into prindex and use @sortas to have overall list appear first in index.

--- a/doc/interpreter/module.mk	Sat Jan 06 17:07:37 2018 -0600
+++ b/doc/interpreter/module.mk	Sun Jan 07 20:02:31 2018 -0800
@@ -147,6 +147,7 @@
   %reldir%/plot.texi \
   %reldir%/poly.texi \
   %reldir%/preface.texi \
+  %reldir%/pr-idx.texi \
   %reldir%/quad.texi \
   %reldir%/set.texi \
   %reldir%/signal.texi \