[Description]
Purge old files from Freedesktop Trash. A path is purged from Trash if formula
expression size^sizepow*age^agepow evaluates to value larger than maximum age.
Ages are expressed in seconds. With default values the comparison expression
evaluates typically in between 1 and 10 times the real age. If you want to purge
just by the age use --size-power=0.

[Conforming to]
http://freedesktop.org/wiki/Specifications/trash-spec