Fix --one-top-level used together with --list.

Fix --one-top-level used together with --list.

* src/extract.c: Move one_top_level stuff to tar.c (decode_options).
* src/tar.c (option_conflict_error): New function.
(decode_options): Use option_conflict_error to complain about
conflicting options in a uniform manner.
Process one_top_level options here.
(request_stdin): Fix error message.
* tests/onetop04.at: New testcase: check --one-top-level with --list.
* tests/Makefile.am: Add new testcase.
* tests/testsuite.at: Add new testcase.