Do not request the status of all entries in the cache. Instead force Finder
to request the ones that it deems necessary by keeping the old statuses
in a separate dictionary which are only used while the new status arrives.
removeIcons isn't called and clearFileNameCacheForPath was always
called with a "nil" path.
Remove the return value of askForIcon which was always 0, and use
that value explicitly at the only call site.
Remove the "-1" code path in iconByPath since setIcons prevents
-1 from getting into _fileNamesCache in all cases.
The client (in this case mirall) tells the Finder plugin where to get the icons.
This enables installation in different locations and in branded clients.
Re-retrieve all icons for a path in case we receive UPDATE_VIEW.
(But in contrast to previous code, don't delete the icons which then
would have caused screen flickering)
