Adding files to gnulib_extra_files in bootstrap.conf?

[John W. Eaton]

The bootstrap script has

# Extra files from gnulib, which override files from other sources.
test -z "${gnulib_extra_files}" && \
  gnulib_extra_files="
        build-aux/install-sh
        build-aux/mdate-sh
        build-aux/texinfo.tex
        build-aux/depcomp
        build-aux/config.guess
        build-aux/config.sub
        doc/INSTALL
"

so it's possible to replace the list of files.  Could we make it easy to 
just add to the default list as well?

I noticed this because I wanted to add build-aux/move-if-change to the 
list but couldn't see how to do that without duplicating the default 
list in my bootstrap.conf file.

Or is this intentional?

jwe