Fix data loss when acting as filter

This bug was introduced by the recent lseek-related changes.
* src/delete.c (delete_archive_members):
* src/update.c (update_archive):
Copy the member if acting as a filter, rather than lseeking over
it, which is possible if stdin is a regular file.
* src/list.c (skim_file, skim_member):
* src/sparse.c (sparse_skim_file):
New functions, for copying when a filter.
* src/list.c (skip_file): Remove; replaced with skim_file.
All callers changed.
(skip_member): Reimplement in terms of skim_member.
* src/sparse.c (sparse_skip_file):
Remove; replaced with sparse_skim_file.  All callers changed.
* src/update.c (acting_as_filter): New static var.
(update_archive): Set it; this is like delete.c.
* tests/delete01.at (deleting a member after a big one):
* tests/delete02.at (deleting a member from stdin archive):
Also test filter case.

src/delete.c

@@ -183,13 +183,13 @@ delete_archive_members (void)
 	case HEADER_SUCCESS:
 	  if ((name = name_scan (current_stat_info.file_name)) == NULL)
 	    {
-	      skip_member ();
+	      skim_member (acting_as_filter);
 	      break;
 	    }
 	  name->found_count++;
 	  if (!ISFOUND (name))
 	    {
-	      skip_member ();
+	      skim_member (acting_as_filter);
 	      break;
 	    }
 	  FALLTHROUGH;