clean up check selection code

This new approach allows filtering out checks from the default set that are
not appropriate for a command, rather than having to list every check
that is appropriate. It also reduces some boilerplate.

Haskell does not define Eq for functions, so I had to go a long way around
with each check having a unique id. Meh.

Command/ConfigList.hs

@@ -11,9 +11,9 @@ import Common.Annex
 import Command
 import Annex.UUID
 
-command :: [Command]
-command = [Command "configlist" paramNothing defaultChecks seek
-		"outputs relevant git configuration"]
+def :: [Command]
+def = [command "configlist" paramNothing seek
+	"outputs relevant git configuration"]
 
 seek :: [CommandSeek]
 seek = [withNothing start]