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.

Git/DiffTree.hs

@@ -78,7 +78,13 @@ getdiff command params repo = do
 	(diff, cleanup) <- pipeNullSplit ps repo
 	return (parseDiffRaw diff, cleanup)
   where
-	ps = command : Params "-z --raw --no-renames -l0" : params
+	ps = 
+		command :
+		Param "-z" :
+		Param "--raw" :
+		Param "--no-renames" :
+		Param "-l0" :
+		params
 
 {- Parses --raw output used by diff-tree and git-log. -}
 parseDiffRaw :: [String] -> [DiffTreeItem]