Redis lua int64

@antire,

I added int64 support for redis lua in this patch. 

Currently, “number" is the only type in lua to define numerical object, which is actually a "double". The integer returned from redis will be conversed to "number"; the return value of "tonumber" lua function is also a "number". However, the conversion from a 64bit "int" to a "double" may cause loss of data.

In some cases, we'd like to use "int64" type, and do some calculation in lua script(i.e. incremental id). So I added this support for redis, and want to merge it to redis, since it is a common requirement. 

Pls let me know if you have any comments, thx.