As Juergen Heinzl pointed out, much of my original fwi calculations evaluated

As Juergen Heinzl pointed out, much of my original fwi calculations evaluated
to zero due to the integer range limitations.  shifting everything to the microsecond
range should solve this problem without introducing ugly floating point arithmetics.

git-svn-id: https://svn.gnumonks.org/trunk/librfid@1425 e0336214-984f-0b4b-a45f-81c69e1f0ede