WeatherPush: Way of retransmitting modified samples

[davidrg]

Bug #141 has resulted in ET data not being transmitted for an unknown length of time. Once the bug is fixed all affected amples need to be retransmitted somehow. WeatherPush currently provides no facility to do this.

• New "retransmit" replication status
• Protocol change to support signaling to the server a retransmission and that any stored copy of the sample should be overwritten.
• Update trigger for the sample tables to alter the replication status whenever a row is modified

Once this is done the ET mess needs fixing:

• Mark all rows at SB with ET data for retransmission
• Check HLZ dataset to make sure no ET data was lost during recent server failures (at one point the Hamilton DB was recreated form a back up of the fremont DB but this may have been before the HLZ station was setup)
• Mark all rows for HLZ with ET data for retransmission