Fix bug in the inplementation of --one-top-level.

Fix bug in the inplementation of --one-top-level.

When extracting an archive that contains './' with the --one-top-level option,
the mode and ownership of '.' would be incorrectly applied to the current
working directory, instead of the requested top-level directory.

* src/list.c (enforce_one_top_level): Map '.' to the top-level
directory.
* tests/Makefile.am: Add onetop05.at
* tests/testsuite.at: Include onetop05.at.
* tests/onetop05.at: New file.
* tests/onetop01.at: Fix keywords.
* tests/onetop02.at: Likewise.
* tests/onetop03.at: Likewise.
* tests/onetop04.at: Likewise.