all: be less strict about usage if POSIX 2008

sort, tail, and uniq now support traditional usage like 'sort +2'
and 'tail +10' on systems conforming to POSIX 1003.1-2008 and later.
* NEWS: Document this.
* doc/coreutils.texi (Standards conformance, tail invocation)
(sort invocation, uniq invocation, touch invocation):
Document new behavior, or behavior's dependence on POSIX 1003.1-2001.
* src/sort.c (struct keyfield.traditional_used):
Rename from obsolete_used, since implementations are now allowed
to support it.  All uses changed.
(main): Allow traditional usage if _POSIX2_VERSION is 200809.
* src/tail.c (parse_obsolete_option): Distinguish between
traditional usage (which POSIX 2008 and later allows) and obsolete
(which it still does not).
* src/uniq.c (strict_posix2): New function.
(main): Allow traditional usage if _POSIX2_VERSION is 200809.
* tests/misc/tail.pl: Test for new behavior.

1 files changed, 8 insertions, 1 deletions

diff --git a/src/uniq.c b/src/uniq.c
index 0e118da9d..896ce938f 100644
--- a/src/uniq.c
+++ b/src/uniq.c
@@ -226,6 +226,13 @@ Also, comparisons honor the rules specified by 'LC_COLLATE'.\n\
   exit (status);
 }
 
+static bool
+strict_posix2 (void)
+{
+  int posix_ver = posix2_version ();
+  return 200112 <= posix_ver && posix_ver < 200809;
+}
+
 /* Convert OPT to size_t, reporting an error using MSGID if OPT is
    invalid.  Silently convert too-large values to SIZE_MAX.  */
 
@@ -533,7 +540,7 @@ main (int argc, char **argv)
           {
             unsigned long int size;
             if (optarg[0] == '+'
-                && posix2_version () < 200112
+                && ! strict_posix2 ()
                 && xstrtoul (optarg, NULL, 10, &size, "") == LONGINT_OK
                 && size <= SIZE_MAX)
               skip_chars = size;