Faulty temperature readings in DS2438 library - ds2438::readTempC() looses sign when shifting data from read

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What steps will reproduce the problem?
1. When the the temperqature drops below zero the sensor gives wrong readings

See: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1289330809/0

What is the expected output? What do you see instead?
expected negative values, see positive

What version of the product are you using? On what operating system?
-

Please provide any additional information below.
In the thread on the forum a solution is proposed by me to change readTempC() 
function to correct the output. This need to be confirmed by someone who has 
such sensor (and a freezer :)
Rob Tillaart

Original issue reported on code.google.com by [email protected] on 10 Nov 2010 at 8:11