timestamp in AMQP-0-9-1 should be seconds other than milliseconds

[johnzhanghua]

As per the spec of AMQP 0-9-1, the timestamp value should be :

4.2.5.4 Timestamps Time stamps are held in the 64-bit POSIX time_t format with an accuracy of one second. By using 64 bits we avoid future wraparound issues associated with 31-bit and 32-bit time_t values.

So the qampqframe.cpp should be changed as the commit

Thanks, John Zhang