idio: unsigned int descriptors vs lognot

[mwette]

This is not a bug per se', but an idiosyncracy that has shown up for me.
In Guile, at least, lognot will return a negative number. That does not bode well for bs unsigned-int.
Is there a clean way to deal with this? Currently I use a clean-up function that takes an integer and a bs descriptor and makes the adjustment, if needed.