Switch -TB<date> - process files modified before the specified date

Process only files modified before the specified date.

Format of the date string is YYYYMMDDHHMMSS. It is allowed to insert separators like '-' or ':' to the date string and omit trailing fields. For example, the following switch is correct: -tb2001-11-20. Internally it will be expanded to -tb20011120000000 and treated as "files modified before 0 hour 0 minutes 0 seconds of 20 November 2001".