[ptx] support for 16 bits in PTmender

[dmg]

Hi everybody,

I just completed full support for 16 bit images in PTmender. 

In the process I updated libpano version to 2.8.3


--
Daniel M. German                  "For indeed who is there alive
                                   that will not be swayed by his
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dmg (at) uvic (dot) ca
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