DATAREDIS-286 - Avoid overflow in JedisConnection#expire / #pexpire.

Workaround Jedis issue https://github.com/xetorthio/jedis/pull/575.
We now delegate calls to expire(...) to pExpireAt(...) in case the seconds parameter is > than Integer.MAX_VALUE.
We query the server time to compute the new expiration date.

Original pull request: #52.