Merge pull request #2050 from matrix-org/rav/federation_backoff

synapse/crypto/keyring.py

synapse/federation/federation_client.py

synapse/federation/transaction_queue.py

synapse/federation/transport/client.py

synapse/handlers/directory.py

synapse/handlers/e2e_keys.py

synapse/handlers/profile.py

synapse/http/matrixfederationclient.py

synapse/util/retryutils.py

tests/handlers/test_directory.py

tests/handlers/test_profile.py

tests/handlers/test_typing.py