Trash spec: directory size cache

[David Faure]

It turns out that the trash spec already uses %-encoding: for the path stored 
in the trashinfo file.

So we discussed it a bit more and came up with this update:

Let's not use the desktop entry standard for this, but a simple text format, 
where each line is:
<size> <mtime> <%-encoded-path>

Technically % encoding is really only necessary for control characters, but if 
we use URL escaping and escape other chars too, who cares, that'll work too.

To resolve the timezone discussion, we'll just use the mtime in number format.
So the file will look like:

16950 15803468 Documents
2467 15803582 Another_Folder

Due to the clash with the KDE "metadata" file (our earlier attempt at caching 
the size, using INI format), this change of format means we should call it 
something else after all, say:

TRASH_DIR/directorysizes

-- 
David Faure, faure at kde.org, http://www.davidfaure.fr
Working on KDE, in particular KDE Frameworks 5