On Linux, use Inotify directly for file notification changes

Use Sebastian Trueg's KInotify wrapper, if Inotify is available.
This gives much more detailed reports and especially info when a file
has been closed after write. For a detailed explanation, see
http://trueg.wordpress.com/2011/10/13/taking-a-break-from-crash-fixing-for-usability/
Separate the file watch code from AlbumManager to a new class, AlbumWatch.
Do not watch directories recursively (convenient API, but often inefficient implementation
out of our reach). We scan the directories anyway, it is possible and efficient to
add each directory = album separately.
If Inotify is not available (non-linux), the previous code based on
KDirWatch and KIO is still used.

CCMAIL: digikam-devel@kde.org