tests: fix maintainer-xml-check.

* data/xslt/xml2dot.xsl (xsl:template match="bison-xml-report"):
Update output to include comments now produced by --graph.
(xsl:template match="automaton"): As for --graph, name the
digraph after the grammar file.
* src/print-xml.c (escape_bufs): Enlarge array.
(print_xml): Add bug-report and url attributes to
bison-xml-report element.