Convert time to the UTC before sending to the server.

This patch improves timestamp support in case like this: https://gist.github.com/vmihailenco/6a7432d7c51c7fa8a718

Before this patch:
2014-03-26 16:31:24.341358434 +0200 EET 2014-03-26 16:31:24.341358 +0200 +0200

After:
2014-03-26 16:43:17.181876703 +0200 EET 2014-03-26 14:43:17.181877 +0000 +0000

Discovered this while working on the https://github.com/vmihailenco/pg/issues/4 . You can take tests there if you want...