manpage-bold-literal.xsl: match for namespaced "d:literal" in template

manpage-bold-literal.xsl: match for namespaced "d:literal" in template

We recently regressed our rendering with Asciidoctor of "literal"
elements in our manpages, i.e, stuff we have placed within `backticks`
in order to render as monospace. In particular, we lost the bold
rendering of such literal text.

The culprit is f6461b82b9 ("Documentation: fix build with Asciidoctor 2",
2019-09-15), where we switched from DocBook 4.5 to DocBook 5 with
Asciidoctor. As part of the switch, we started using the namespaced
DocBook XSLT stylesheets rather than the non-namespaced ones. (See
f6461b82b9 for more details on why we changed to the namespaced ones.)

The bold literals are implemented as an XSLT snippet <xsl:template
match="literal">...</xsl:template>. Now that we use namespaces, this
doesn't pick up our literals like it used to.

Match for "d:literal" in addition to just "literal", after defining the
d namespace. ("d" is what
http://docbook.sourceforge.net/release/xsl-ns/current/manpages/docbook.xsl
uses.) Note that we need to keep matching without the namespace for
AsciiDoc.

This boldness was introduced by 5121a6d993 ("Documentation: option to
render literal text as bold for manpages", 2009-03-27) and made the
default in 5945717009 ("Documentation: bold literals in man",
2016-05-31).

One reason this was not caught in review is that our doc-diff tool diffs
without any boldness, i.e., it "only" compares text. As pointed out by
Peff in review of this patch, one can use `MAN_KEEP_FORMATTING=1
./doc-diff <...>`

This has been optically tested with AsciiDoc 8.6.10, Asciidoctor 1.5.5
and Asciidoctor 2.0.10. I've also verified that doc-diff produces the
empty output for all three programs, as expected, and that with the
MAN_KEEP_FORMATTING trick, AsciiDoc yields no diff, whereas with
Asciidoctor, we get bold literals, just like we want.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Acked-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>