core: Handle exceptions when releasing the interfaces.
core: Handle exceptions when releasing the interfaces.

At object destruction, claimed interfaces are released. If the device
is disconnected, the call to release_interface may fail and raise an
exception.

closes #84.

AlanJAS/pyusb,rabryan/pyusb,h3nj3/pyusb,karlp/pyusb,makerbot/pyusb,karlp/pyusb,h3nj3/pyusb,rabryan/pyusb,swinman/pyusb,kopchik/pyusb,makerbot/pyusb,kopchik/pyusb,swinman/pyusb,AlanJAS/pyusb