Use a bool in struct cgpu to know when a usb device has been blacklisted, avoiding blacklisting it more than once.
Add the ability to whitelist previously blacklisted usb devices from the menu.
Prevent recursive loop in __is_in_use linked list walking.
Allow hotplug interval to be changed from the USB menu.
Merge pull request #549 from kanoi/master

bab - handle disabling chips that return no valid results
Detect non-responsive bitfury devices and try a usb reset on them before killing their instances off after 2 minutes of no activity.
Detect non-responsive icarus devices and attempt a usb reset before killing them after 2 minutes of no hashes.
Merge branch 'master' of github.com:ckolivas/cgminer
Check for hfa invalid hash clockrate after other error messages.