added tablex.previous_element

tablex.lua

@@ -182,6 +182,20 @@ function tablex.next_element(t, v)
 	return t[i]
 end
 
+function tablex.previous_element(t, v)
+	local i = tablex.index_of(t, v)
+	--not present? just get the front of the table
+	if not i then
+		return tablex.front(t)
+	end
+	--(not using mathx to avoid inter-dependency)
+	i = i - 1
+	if i == 0 then
+		i = #t
+	end
+	return t[i]
+end
+
 --note: keyed versions of the above aren't required; you can't double
 --up values under keys