Darwin: Return error code in darwin_error_str() on unknown error

* Closes #117
Darwin: Fix a SIGFPE

* GetPipeProperties() may fail when the device is unplugged if DeviceVersion is not greater than 320.
* In this case maxPacketSize will be zero and the integer division will throw a EXC_ARITHMETIC signal.
* Closes #136
Darwin: Fix format of 64-bit sessionIDs in log messages

* The sessionID value is 64-bit, so print it as such.
* Closes #153