Line numbers missing from \show output if \showstream sends to a file

Hi,

I visited pipermail/tex-live and saw a previous message
by Joseph Wright on \showstream.

I go interested
as the return status of the pdftex/pdflatex run
will not be 1 if \showstream corresponds to a real
file opened by \openout.  Which is interesting if
using latexmk for example (if with LaTeX format).
This can be very useful for setting up test suites.

Also, as the stuff is
sent to another file than the log, Emacs/AUCTeX
does not think there was an error.

On trying it out I noticed though that the information
sent to external file by \show, \showbox,
does not include the line numbers.

---- example output to external file
test

> \foo=undefined

> \box0=
\hbox(0.0+6.00006)x8.75002
.\tenex B



! OK

bong
----

In practice when debugging, one has only one or two
\show's which one placed deliberately in the source
file, so it is not real inconvenience.  But still,
having more information is always good especially
in the context of scripting.

Any reason for no line numbers?

Source for the above example:

\immediate\openout1=test.txt
\immediate\write1{test}
\showstream1   % A real file
%\showstream16  % or 128 for LuaTeX
\show\foo
\showbox0
\immediate\write\showstream{^^Jbong}
\bye


Best,

Jean-François
PS I am sorry I am not subscribed to the list, but I
don't expect to have anything of relevance to say 
from that point on anyhow, so I will read later on pipermail
if the thread evolves. (I recently made much noise on some
TeX memory thing but I expect to stay put this time).