[tex-eplain] Treat \refn as a number?

[Karl Berry]

    with a number, say 2, using \ifnum, I have troubles: if I say, e.g.,

    \ifnum2=\refn{label2}yes\else no\fi

Yeah, \refn is not even close to expandable.

It's been a lot of years since I wrote this code, but looking at
xeplain.tex, it might be possible to use \xrlabel?  Something like:
\expandafter\ifnum\csname\xrlabel{label}\endcsname\endcsname = 2

Untested, probably have to experiment.  I don't even remember for sure
that the xref label is defined simply as a number, or if more control
sequences intervene.

HTH,
k