libusb port: Support transfer timeouts

[emaxx-google]

Currently, the transfer timeouts are handled like a transfer error.

This comes through a number of places in the code. One example is the code that talks to chrome.usb: the chrome.usb API returns the error "Transfer timed out." in case of timeouts (just like any other error). We should do the string comparison there in order to distinguish the transfer timeouts from any other errors.

This is a very low-priority item, as it's not affecting any functionality in CCID or PC/SC-Lite (the CCID itself treats timeouts similarly to other errors).