let optparse-applicative handle the usage display when run w/o command or bad command

Still generating the list of commands myself, to get it sorted into
sections and with short synopses.

CmdLine/GitAnnex.hs

@@ -19,6 +19,7 @@ import qualified Command.Add
 import qualified Command.Unannex
 import qualified Command.Fsck
 {-
+import qualified Command.Help
 import qualified Command.Drop
 import qualified Command.Move
 import qualified Command.Copy
@@ -97,7 +98,6 @@ import qualified Command.Proxy
 import qualified Command.DiffDriver
 import qualified Command.Undo
 import qualified Command.Version
-import qualified Command.Help
 #ifdef WITH_ASSISTANT
 import qualified Command.Watch
 import qualified Command.Assistant
@@ -124,6 +124,7 @@ cmds =
 	[ Command.Add.cmd
 	, Command.Fsck.cmd
 {-
+	, Command.Help.cmd
 	, Command.Get.cmd
 	, Command.Drop.cmd
 	, Command.Move.cmd
@@ -204,7 +205,6 @@ cmds =
 	, Command.DiffDriver.cmd
 	, Command.Undo.cmd
 	, Command.Version.cmd
-	, Command.Help.cmd
 #ifdef WITH_ASSISTANT
 	, Command.Watch.cmd
 	, Command.Assistant.cmd
@@ -224,9 +224,6 @@ cmds =
 -}
 	]
 
-header :: String
-header = "git-annex command [option ...]"
-
 run :: [String] -> IO ()
 run args = do
 #ifdef WITH_EKG
@@ -234,7 +231,9 @@ run args = do
 #endif
 	go envmodes
   where
-	go [] = dispatch True args cmds gitAnnexOptions [] header Git.CurrentRepo.get
+	go [] = dispatch True args cmds gitAnnexOptions [] Git.CurrentRepo.get
+		"git-annex"
+		"manage files with git, without checking their contents in"
 	go ((v, a):rest) = maybe (go rest) a =<< getEnv v
 	envmodes =
 		[ (sshOptionsEnv, runSshOptions args)

CmdLine/GitAnnexShell.hs

@@ -101,7 +101,9 @@ builtin cmd dir params = do
 	let (params', fieldparams, opts) = partitionParams params
 	    rsyncopts = ("RsyncOptions", unwords opts)
 	    fields = rsyncopts : filter checkField (parseFields fieldparams)
-	dispatch False (cmd : params') cmds options fields header mkrepo
+	dispatch False (cmd : params') cmds options fields mkrepo
+		"git-annex-shell"
+		"Restricted login shell for git-annex only SSH access"
   where
 	mkrepo = do
 		r <- Git.Construct.repoAbsPath dir >>= Git.Construct.fromAbsPath

CmdLine/Usage.hs

@@ -13,9 +13,12 @@ import Types.Command
 usageMessage :: String -> String
 usageMessage s = "Usage: " ++ s
 
-{- Usage message with lists of commands by section. -}
 usage :: String -> [Command] -> String
-usage header cmds = unlines $ usageMessage header : concatMap go [minBound..]
+usage header cmds = unlines $ usageMessage header : commandList cmds
+
+{- Commands listed by section, with breif usage and description. -}
+commandList :: [Command] -> [String]
+commandList cmds = concatMap go [minBound..]
   where
 	go section
 		| null cs = []
@@ -39,6 +42,7 @@ usage header cmds = unlines $ usageMessage header : concatMap go [minBound..]
 	longest f = foldl max 0 $ map (length . f) cmds
 	scmds = sort cmds
 
+
 {- Descriptions of params used in usage messages. -}
 paramPaths :: String
 paramPaths = paramRepeating paramPath -- most often used