Fix interval-based rotations when the -t flag is used. In this case, find the most-recently archived logfile and use its mtime to determine whether or not to rotate, as in the non-timestamped case.
Fix interval-based rotations when the -t flag is used. In this case, find
the most-recently archived logfile and use its mtime to determine whether
or not to rotate, as in the non-timestamped case.

Previously we would just try to use the mtime of <logfile>.0, which always
results in a rotation since it generally doesn't exist in the -t case.

PR:		bin/166448
Approved by:	emaste (co-mentor)
Tested by:	Marco Steinbach <coco executive-computing.de>
MFC after:	2 weeks

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