Fix create_at_logtime with recreate_check_signal

In Appender::File, with create_at_logtime and recreate_check_signal both
enabled, log file never gets opened, resulting in error:

  Can't use an undefined value as a symbol reference at
  .../Log/Log4perl/Appender/File.pm line 244.
Unlink additional testfile
Merge pull request #28 from tamias/master

Fix create_at_logtime with recreate_check_signal