Primary change better U3 support

Human readable changelog:

- Antminer U1 support
- Numerous fixes for behaviour surrounding USB errors - pipe and IO errors, and no more attempting to reset the device since it's rarely helpful and occasionally harmful.
- Libusb and libusbx have finally reconciled their differences and merged all their fixes together into a new official libusb release, so the main change in this version is updating the core code to include this latest libusb. Hopefully this might increase compatibility with some USB3 hubs on windows and make it more reliable (based on the changelogs I can see in libusb). This is the reason for the minor version number update to 12 as it's quite a substantial code change, hopefully only for the better!
- Increased the hashfast overheat limit default to 90 after extensive discussions with the engineers who designed the devices.
- Fixed a crash in the nanofury USB stick code.
- Fixed the displayed diff shown being wrong when solo mining.
- bab driver fixes courtesy of Kano.


Full changelog:

- Add support for AntminerU1 devices with the icarus driver.
- Add antminer U1 to comment in udev rules.
- Do away with usb resets entirely since we retry on both pipe and io errors now
and they're of dubious value.
- Retry on usb IO errors instead of faking success.
- Check that we've cleared the pipe error after a clear request, not the err
value which is unchanged.
- Update to libusb-1.0.18
- Change hfa overheat limit to 90 degrees.
- Relax timeout in hf get header to 500ms to match the usb timeout.
- Minion - check/clear interrupts for all chips
- Set info work to null after it is freed in nf1 after a restart to prevent
double free later.
- The second_run bool in libbitfury should be per device. Microoptimise its and
job_switched usage, removing the unused results array for NF1 devices.
- Fix displayed diff when solo mining at >2^32 diff.
- bab - stop stale work accumulating
- bab - set the default SPI speed back to 96000

Most of the changes are HashFast related:

- A proper working hashfast driver tested working on a real device, including the windows version.
- Substantially updated BAB driver courtesy of Kano. Hopefully he can give us a summary of the changes there.
- Generic fixes for the reconnect bug on btcguild (unsure if other issues still exist).
- Work is discarded on a stratum reconnect message from the pool now (as btcguild uses) to avoid working on invalid work on switching URLs.
- Fixed the stuck line at the top of the log window.
- Message about block change detected no longer mentions longpoll.
- API now has a field "Last getwork" in summary which can be used to see that we are still getting work from pools. This is useful if you are trying to determine if a device is dead for device reasons or simply isn't getting work from any pools. It uses the same numbering in seconds with the "Last Valid Work" returned in the device API. If "Last getwork" is not incrementing, there is no work for any devices.
- Added a --nfu-bits command to allow you to set the clock speed on nanofury/icefury usb sticks. Note that the default was 54 so is now 50 to be in keeping with USB2 power limit standards. This means IT WILL BE SLOWER compared to 3.10.0 unless you change it with this option back to 54. The driver is otherwise unchanged so any other differences you see are pure variance.
- Threads names have been changed so they will show up with different, consistent names in your process manager of choice.
- Building will now not include libbitfury on every configuration unnecessarily.
- The crash on device removal has been fixed.
- Fixes for lean configurations that failed to build.

- Hashfast driver changes:
-- Should be more robust with respect to initialisation and dropouts
-- If the device stops returning shares, cgminer will reset the device, and if it cannot, it will drop it, which usually allows it to be re-hotplugged again.
-- If a device needs to be reset for not returning shares, and the clockspeed is still overclocked, cgminer will lower the clocks further on every reset.
-- Devices will be throttled if they reach 85 degrees. With water cooling they usually drop in temperature very rapidly. This can be configured with --hfa-temp-overheat
-- Hashrate displayed will be based on valid shares returned so should more accurately represent what the pool will see you hashing at. It will look very unstable initially. Earlier boards do have some loss so the previously displayed hashrate was always over. You can compare the total hashes estimated by this as "Calc hashcount" to compare with "Raw hashcount" the device has worked on in the API stats to see how they differ.
-- Max temp on screen will not show if it's an obvious error showing something like 512
-- The API will show board temperatures
-- Windows builds work
-- Babyjets show up as HFB while Sierras show up as HFS. Custom devices will come up with the generic HFA name. Note that if you are trying to select them with the --usb command, they are all seen as HFA due to the fact that cgminer can only tell them apart after they have been initialised and running.

- Minion driver courtesy of Kano. (More info about this from him hopefully).
- Nanofury driver. These are set up the same as every other USB device is on cgminer. Tested on both windows and linux (sorry no osx to test). Note the hashrate is once again based on only valid shares so may appear lower than other software using this device. No HW errors are currently counted (though they're most definitely there in abundance due to bitfury design). This is a driver based on all the other ones out there with a completely rewritten model to suit how cgminer drivers work. 
- Hashfast driver fixes (no I still don't have one).
- Fixed BXF devices slowing down over time.