ThreadLocalScope doesn't clear manually set Keys

Manually bound Keys end up caching a value you might expect to be thread local with ThreadLocalScope. The problem is that for manually bound items, a InstanceProvider(to) is created. Then later ThreadLocalScope does

provider = InstanceProvider(provider.get(self.injector))

Where provider.get just returns that to always. I would have expected something fancier to happen such that thread2 would never see the binding.

TEST_KEY = Key('TEST_KEY')

thread1
injector.binder.bind(TEST_KEY, 'test', threadlocal)
assert(injector.get(TEST_KEY) == 'test')

thread2

assert(injector.get(TEST_KEY) == 'test')

https://github.com/alecthomas/injector/blob/master/injector.py#L442
https://github.com/alecthomas/injector/blob/master/injector.py#L608

Not really sure what the best approach would be. I would have thought that the thread local scope sort of owned the binding created when I did

injector.binder.bind(TEST_KEY, 'test', threadlocal)

Start in injector.py around lines 442 and 608, focusing on ThreadLocalScope and the InstanceProvider created for manually bound Keys. Reproduce the two-thread example from the issue and inspect how provider.get(self.injector) handles the manually supplied value. Done means a manually thread-local-bound Key is not visible across threads, with regression coverage for that behavior.