xml: match DOT output and xml2dot.xsl processing

xml: match DOT output and xml2dot.xsl processing

Make the DOT produced by XSLT processing equivalent to the one made with the
--graph option.

* data/xslt/xml2dot.xsl: Stylistic changes, and add support for reductions.
* doc/bison.texi (Xml): Update.
* src/graphviz.c (conclude_red): Minor stylistic changes to DOT internals.
(output_red): Swap enabled and disabled reductions output, for coherence
with XSLT output.
* src/print_graph.c (print_core): Minor stylistic change to States' output.
(print_actions): Swap order of output for reductions and transitions.
* tests/local.at (AT_BISON_CHECK_XML): Ignore differences in order.
* tests/output.at: Adjust to changes in DOT internals.