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/CheckIgnore.hs

@@ -43,7 +43,10 @@ checkIgnoreStart repo = ifM supportedGitVersion
   where
 	params =
 		[ Param "check-ignore" 
-		, Params "-z --stdin --verbose --non-matching"
+		, Param "-z"
+		, Param "--stdin"
+		, Param "--verbose"
+		, Param "--non-matching"
 		]
 	repo' = repo { gitGlobalOpts = filter (not . pathspecs) (gitGlobalOpts repo) }
 	pathspecs (Param "--literal-pathspecs") = True