Reduce memory consuption when handling the -T option.

The commit cdb27293 made the -T option more flexible, but
incurred a very considerable memory overhead by storing
all file names in the argument array.  In case of very
big file lists this caused tar to run out of memory.  This
was reported by Christian Wetzel <wetzel@phoenix-pacs.de>
on March 14, 2013
(http://lists.gnu.org/archive/html/bug-tar/2013-03/msg00018.html).

On the other hand, Michal Žeidl discovered that tar misfunctioned
when given empty file lists or lists with the trailing newline
misssing in the last entry.  This was reported by Pavel Raiskup
on July 23
(http://lists.gnu.org/archive/html/bug-tar/2013-07/msg00009.html and
msg00010.html).

This change fixes both issues.

* src/common.h (name_add_file,request_stdin): New prototype.
(more_options): New prototype.
* src/names.c (NELT_FILE): New entry type.
(name_elt) <file>: New union member.
(name_add_file): New function.
(read_name_from_file): New function, a rewrite of
the same function from tar.c
(read_next_name,copy_name): New static functions.
(name_next_elt): Handle NELT_FILE entries.
* src/tar.c (request_stdin): Make extern.
(read_name_from_file,add_file_id)
(update_argv): Removed.
(parse_opt): Change handling of the -T option.
(more_options): New function.

* tests/T-null.at: Rewrite test.
* tests/T-zfile.at: New file.
* tests/T-nonl.at: New file.
* tests/Makefile.am: Add new testcases.
* tests/testsuite.at: Likewise.

* THANKS: Update.
Bugfix.

* src/names.c (read_name_from_file): Fix a typo. Remove
unused variable.
Fix interacton of --verbose and --append.

* src/buffer.c (_open_archive): don't overwrite existing archive
if given the --verify option.
* tests/append04.at: New file.
* tests/Makefile.am: Add new testcase.
* tests/testsuite.at: Add new testcase.
* THANKS: Update.
Update the docs.

* doc/tar.texi: Parsing of the options found in the file list
follows the same rules as for command line.  Remove the obsolete
description.  This complements 26538c9b.
Minor changes

* src/names.c (handle_option): Use program_invocation_short_name
instead of the constant string.
(read_next_name): Remove unused variable.
Fix use of uninitialized memory

* src/names.c (name_add_file): Initialize the ep->v.file.fp pointer
after structure allocation.
Minor change.

* src/names.c (name_next_elt): Simplify conditional.
Don't treat attempts to read an already read file list as fatal errors.

* src/names.c (add_file_id): Report error and return 1 if the file
has already been read.
(read_next_name): Don't try to open file if add_file_id returns 1.
(name_next_elt): Simplify conditional.
Revamp initial name collection functions to ensure proper argument ordering.

* src/names.c (NELT_NOOP): New constant
(name_elt) <next,prev>: New members.
(name_array,allocated_entries,entries,scanned): Remove.
(check_name_alloc): Remove function.
(name_elt_alloc): New static.
(name_list_adjust,name_list_advance): New functions.
(name_add_name,name_add_dir)
(name_add_file): Use new allocation functions.
(read_next_name): Advance list head pointer as necessary
before returning.
(name_next_elt): Read elements from list.
* tests/T-cd.at: New file.
* tests/T-mult.at: New file.
* tests/T-nest.at: New file.
* tests/Makefile.am: Add new testcases.
* tests/testsuite.at: Likewise.
Improve error diagnostics

* src/names.c (file_list_name): New static function.
(add_file_id): If a filelist is being read twice, print the names
of the files that caused it.
* tests/T-rec.at: New test case.
* tests/Makefile.am: Add new file.
* tests/testsuite.at: Include new file.
Minor fix in the testsuite.

* tests/T-cd.at: sort the 'tar cf' output.