gettext 0.15 complains about \v in strings, but argp uses \v

[Paul Eggert]

GNU tar 1.15.91 <ftp://alpha.gnu.org/gnu/tar/tar-1.15.91.tar.gz>
contains a file src/tar.c that has the declaration quoted at the end
of this message.  This declaration contains a string of the form
N_("...\v...").  GNU gettext 0.15, unlike earlier versions of GNU
gettext, complains about the \v:

   $ cd tar-1.15.91/src
   $ xgettext --keyword=N_ tar.c
   ../../../gettext-0.15/gettext-tools/src/xgettext.c:2038: internationalized 
messages should not contain the `\v' escape sequence

The \v is needed by argp: argp uses it to split the diagnostic into
two pieces, which are formatted differently; the \v is never sent to
the user.  (I'm not a fan of this interface -- I'm just describing
it....)

Is there some reason for this new restriction in gettext 0.15?  I
searched the gettext 0.15 manual for instances of "\v", and didn't see
anything relevant.  It's not clear to me why the restriction is
needed, as the C escapes \a \b \f \n \r \t \v should all be fairly
portable these days.

PS.  This message follows up on a thread that started in bug-tar at
<http://lists.gnu.org/archive/html/bug-tar/2006-08/msg00016.html>,
and I'm CC'ing it to bug-tar.

======

static char doc[] = N_("GNU `tar' saves many files together into a single tape 
or disk archive, and can restore individual files from the archive.\n\
\n\
Examples:\n\
  tar -cf archive.tar foo bar  # Create archive.tar from files foo and bar.\n\
  tar -tvf archive.tar         # List all files in archive.tar verbosely.\n\
  tar -xf archive.tar          # Extract all files from archive.tar.\n\
\vThe backup suffix is `~', unless set with --suffix or SIMPLE_BACKUP_SUFFIX.\n\
The version control may be set with --backup or VERSION_CONTROL, values 
are:\n\n\
  none, off       never make backups\n\
  t, numbered     make numbered backups\n\
  nil, existing   numbered if numbered backups exist, simple otherwise\n\
  never, simple   always make simple backups\n");