move supportedBackends list into annex monad

This was necessary so the File backend could import Backend w/o a cycle.

Moved code that checks whether enough backends have a file into File
backend.

Commands.hs

@@ -16,7 +16,6 @@ import qualified Annex
 import Utility
 import Locations
 import qualified Backend
-import BackendList
 import UUID
 import LocationLog
 import Types
@@ -169,10 +168,6 @@ dropCmd file = notinBackend file err $ \(key, backend) -> do
 	if (not inbackend)
 		then return () -- no-op
 		else do
-			force <- Annex.flagIsSet Force
-			if (not force)
-				then requireEnoughCopies key
-				else return ()
 			success <- Backend.removeKey backend key
 			if (success)
 				then cleanup key
@@ -235,51 +230,8 @@ logStatus key status = do
 	gitAdd f Nothing -- all logs are committed at end
 
 inBackend file yes no = do
-	r <- liftIO $ Backend.lookupFile file
+	r <- Backend.lookupFile file
 	case (r) of
 		Just v -> yes v
 		Nothing -> no
 notinBackend file yes no = inBackend file no yes
-
-{- Checks remotes to verify that enough copies of a key exist to allow
- - for a key to be safely removed (with no data loss), and fails with an
- - error if not. -}
-requireEnoughCopies :: Key -> Annex ()
-requireEnoughCopies key = do
-	g <- Annex.gitRepo
-	let numcopies = read $ Git.configGet g config "1"
-	remotes <- Remotes.withKey key
-	if (numcopies > length remotes)
-		then error $ "I only know about " ++ (show $ length remotes) ++ 
-			" out of " ++ (show numcopies) ++ 
-			" necessary copies of: " ++ (keyFile key) ++
-			unsafe
-		else findcopies numcopies remotes []
-	where
-		findcopies 0 _ _ = return () -- success, enough copies found
-		findcopies _ [] bad = die bad
-		findcopies n (r:rs) bad = do
-			result <- liftIO $ try $ haskey r
-			case (result) of
-				Right True	-> findcopies (n-1) rs bad
-				Right False	-> findcopies n rs bad
-				Left _		-> findcopies n rs (r:bad)
-		haskey r = do
-			-- To check if a remote has a key, construct a new
-			-- Annex monad and query its backend.
-			a <- Annex.new r
-			(result, _) <- Annex.run a (Backend.hasKey key)
-			return result
-		die bad =
-			error $ "I failed to find enough other copies of: " ++
-				(keyFile key) ++
-				(if (0 /= length bad) then listbad bad else "")
-				++ unsafe
-		listbad bad = "\nI was unable to access these remotes: " ++
-				(Remotes.list bad) 
-		unsafe = "\n" ++
-			"  -- According to the " ++ config ++
-			" setting, it is not safe to remove it!\n" ++
-			"     (Use --force to override.)"
-
-		config = "annex.numcopies"