Redis LUA stuff

set_save_ex.lua

-- Sets KEY to VALUE, preserving any existing TTL
-- Call with EVAL "..." 1 KEY VALUE
-- or 
-- LOAD SCRIPT "..."
-- => <SHA1>
-- EVALSHA <SHA1> 1 KEY VALUE

local ttl = redis.pcall('ttl', KEYS[1])
if ttl == -1 then
         return redis.pcall('set', KEYS[1], ARGV[1])
else
         return redis.pcall('set', KEYS[1], ARGV[1], 'ex', ttl)
end