remove Params constructor from Utility.SafeCommand

This removes a bit of complexity, and should make things faster
(avoids tokenizing Params string), and probably involve less garbage
collection.

In a few places, it was useful to use Params to avoid needing a list,
but that is easily avoided.

Problems noticed while doing this conversion:

	* Some uses of Params "oneword" which was entirely unnecessary
	  overhead.
	* A few places that built up a list of parameters with ++
	  and then used Params to split it!

Test suite passes.

Command/Uninit.hs

@@ -37,7 +37,7 @@ check = do
   where
 	current_branch = Git.Ref . Prelude.head . lines <$> revhead
 	revhead = inRepo $ Git.Command.pipeReadStrict
-		[Params "rev-parse --abbrev-ref HEAD"]
+		[Param "rev-parse", Param "--abbrev-ref", Param "HEAD"]
 
 seek :: CommandSeek
 seek ps = do