convert notBareRepo to a CommandCheck

This avoids some small overhead by only running the check once per command;
it also ensures that, even if the command doesn't find anything to run on,
it still fails to run when in a bare repo.

Command.hs

@@ -17,7 +17,6 @@ module Command (
 	doCommand,
 	whenAnnexed,
 	ifAnnexed,
-	notBareRepo,
 	isBareRepo,
 	numCopies,
 	numCopiesCheck,
@@ -97,12 +96,6 @@ whenAnnexed a file = ifAnnexed file (a file) (return Nothing)
 ifAnnexed :: FilePath -> ((Key, Backend) -> Annex a) -> Annex a -> Annex a
 ifAnnexed file yes no = maybe no yes =<< Backend.lookupFile file
 
-notBareRepo :: Annex a -> Annex a
-notBareRepo a = do
-	whenM isBareRepo $
-		error "You cannot run this subcommand in a bare repository."
-	a
-
 isBareRepo :: Annex Bool
 isBareRepo = fromRepo Git.repoIsLocalBare