[aprssig] Sub-zero temps on findU

[Steve Dimse]

Crossed another thing off the do list today. For those who chose to live in
places where it gets really cold (though I certainly will never understand why),
the temp graphs should now go lower in cold weather. This isn;t true
autoscaling, rather if any temps go below zero, the graph shifts from 120 -> -10
to 80 -> -50. Let me know if you find any bugs. An example of a cold place:

http://www.findu.com/cgi-bin/wxpage.cgi?call=VE4GLS&last=240

Steve K4HG