1. When size limit is used, a file bigger than the trash size can't be
trashed anymore (a warning message is shown).
2. When size limit is used and warning policy selected, files can't be
trashed anymore if the total size of the trash will exceed the set size
(a warning message is shown).
3. When the trash size settings are modified, the content of the trash
is adjusted based on the new settings.
4. Fixed load/saving of trash options when more than one trash folder exists.
Signed-off-by: Michele Calgaro <michele.calgaro@yahoo.it>