gnulib is no longer an hg subrepo

[John W. Eaton]

After this change (on stable, merged with default):

  http://hg.savannah.gnu.org/hgweb/octave/rev/ece72b94486f

the gnulib sources are no longer managed within the Octave mercurial 
archive as an hg subrepo.  Instead, we now have the bootstrap script 
fetching a copy of gnulib using git.

After updating the Octave sources to get this change you will need to 
remove the gnulib subdirectory in your source tree and run bootstrap to 
pull a new copy of gnulib from upstream (commands executed at the 
top-level of the Octave source tree):

  hg pull -u
  rm -rf gnulib
  ./bootstrap

The gnulib revision is now stored in the bootstrap.conf file instead of 
.hgsubstate.  You may override this revision by setting GNULIB_REVISION 
in the environment when you run the bootstrap script.  For example (bash 
syntax):

  GNULIB_REVISION=8cb410df8b66d3bd0fe43ef580a9f912cc402a96 ./bootstrap

If the revision is empty, bootstrap will use whatever the current 
revision is in your gnulib directory.

Note that the specified revision must be present in your gnulib source 
tree.  If it is not, then bootstrap will fail to set the revision until 
you update your gnulib sources from upstream so that it includes the 
revision you are requesting.  This limitation is a feature imposed by 
the bootstrap script that we inherit from gnulib.  If it turns out to be 
inconvenient or confusing, we may attempt to make updates happen 
automatically when the requested revision is not present.

You may also continue to use an external copy of gnulib by using the 
--gnulib-srcdir option:

  ./bootstrap --gnulib-srcdir=/path/to/gnulib

See also the following bug report:

  https://savannah.gnu.org/bugs/?57044

jwe