proper fix for dropunused

Now getKeysPresent checks that the key's content, not only its directory,
exists. In direct mode, the inode cache file is used as a standin for the
content.

removeAnnex always removes the inode cache file, and drop and move --from
always call removeAnnex, even if the object does not seem to be inAnnex,
to ensure it's always deleted.

Command/Drop.hs

@@ -60,7 +60,7 @@ performLocal key numcopies knownpresentremote = lockContent key $ do
 	untrusteduuids <- trustGet UnTrusted
 	let tocheck = Remote.remotesWithoutUUID remotes (trusteduuids'++untrusteduuids)
 	stopUnless (canDropKey key numcopies trusteduuids' tocheck []) $ do
-		whenM (inAnnex key) $ removeAnnex key
+		removeAnnex key
 		next $ cleanupLocal key
 
 performRemote :: Key -> Maybe Int -> Remote -> CommandPerform