use # length operator instead of string.len (canonicalize)

Used this perl command:

$ # perl -pi -e 's/string\.len\((.*?)\)/#\1/g' *.lua

Also fixed one instance where the above command didn't correctly
translate the intended code (string.len(a .. b .. c)).

nselib/match.lua

@@ -47,7 +47,7 @@ end
 numbytes = function(num)
 	local n = num
 	return function(buf)
-		if(string.len(buf) >=n) then
+		if(#buf >=n) then
 			return n, n
 		end
 		return nil