tar: invalidate directory cache after failed open

tar: invalidate directory cache after failed open

fdbase_opendir copies a requested directory name into the cache before
opening it.  If open_subdir fails, this leaves the new name associated
with the old file descriptor.  A retry after tar creates the missing
parent can then extract into the old directory.

Close an unowned old descriptor before trying to open the new dir and
invalidate the cache entry if that fails.  Add a regression test using
equal-length sibling directory names.

* src/misc.c (fdbase_opendir): Invalidate the cache after a failed
replacement open.
* tests/extrac35.at: New test.
* tests/Makefile.am (TESTSUITE_AT): Add it.
* tests/testsuite.at: Include it.