Because the category makes the protocol apply to all `NSMutableDictionaries`, it can't assume keys are `NSString`. Because these types are covariant, the change is not breaking.

Fix "+ +" typo in Python test harness.

Made insecure channel/stub explicit, in all layers

Re-cutting the 0.12 release from master.

Added support for ResponseParameters.interval_us to the Node interop server

Allow period in header names

Fix proxy end2end tests

Capture latency trace for ping pong during performance runs

Improve MetadataCredentials test

Fix server.KillAsync() and improve abandoned call test

C# test restructuring

- More robustly run processes in the background
- Detect and use pypy if available
- Add a --latency_profile flag to control whether to run the latency profiling stuff

Add test to check that all settings frames are acked

Fix build

Add tests for failed SSL connections: bad cert, and bad alpn config

Increased round robin coverage

Allows http(s)cli_test's server.py override.

Python version bump

run_lcov.sh fix

So that it can be invoked with no arguments