bug#11245: 24.0.95; set-file-selinux-context fails when the filesystem doesn't support contexts

[Glenn Morris <rgm@gnu.org>]

I tested this patch with the scenario you describe (using
backup-by-copying = t) and it works for me. I will commit it soon.

*** src/fileio.c	2012-02-25 09:07:23 +0000
--- src/fileio.c	2012-04-20 17:26:15 +0000
***************
*** 2046,2052 ****
      {
        /* Set the modified context back to the file. */
        fail = fsetfilecon (ofd, con);
!       if (fail)
  	report_file_error ("Doing fsetfilecon", Fcons (newname, Qnil));
  
        freecon (con);
--- 2046,2052 ----
      {
        /* Set the modified context back to the file. */
        fail = fsetfilecon (ofd, con);
!       if (fail && errno != ENOTSUP)
  	report_file_error ("Doing fsetfilecon", Fcons (newname, Qnil));
  
        freecon (con);
***************
*** 2920,2926 ****
  	  /* Set the modified context back to the file. */
  	  fail = lsetfilecon (SSDATA (encoded_absname),
  			      context_str (parsed_con));
! 	  if (fail)
  	    report_file_error ("Doing lsetfilecon", Fcons (absname, Qnil));
  
  	  context_free (parsed_con);
--- 2920,2926 ----
  	  /* Set the modified context back to the file. */
  	  fail = lsetfilecon (SSDATA (encoded_absname),
  			      context_str (parsed_con));
! 	  if (fail && errno != ENOTSUP)
  	    report_file_error ("Doing lsetfilecon", Fcons (absname, Qnil));
  
  	  context_free (parsed_con);