<xref> vs <command> formatting in the docs

Hi Hackers,

While looking at making more <command>SQL</command> into links, I
noticed that <xref> loses the monospace formatting of <command>, and
can't itself be wrapped in <command>.  This becomes particularly
apparent when you have one link that can be an <xref/> next to another
that's <link><command>...</command></link> because it's actually
referring to a specific variant of the command.

By some trial and error I found that putting <command> inside the
<refentrytitle> tag propagates the formatting to the <xref> contents.
We already do this with <application> for (most of) the client and
server applications.  Is this something we want to do consistently for
both?

- ilmari
-- 
"The surreality of the universe tends towards a maximum" -- Skud's Law
"Never formulate a law or axiom that you're not prepared to live with
 the consequences of."                              -- Skud's Meta-Law