move commandAction out of CmdLine.Seek

This is groundwork for nested seek loops, eg seeking over all files and
then performing commandActions on a list of remotes, which can be done
concurrently.

This commit was sponsored by Boyd Stephen Smith Jr. on Patreon.

Command/DiffDriver.hs

@@ -19,7 +19,7 @@ cmd = dontCheck repoExists $
 		("-- cmd --") (withParams seek)
 
 seek :: CmdParams -> CommandSeek
-seek = withWords start
+seek = withWords (commandAction . start)
 
 start :: [String] -> CommandStart
 start opts = do