Update databases/py-cassandra-driver to 2.7.1.

2.7.1

Bug Fixes
- Explicitly include extension source files in Manifest

2.7.0

Cython is introduced, providing compiled extensions for core modules,
and extensions for optimized results deserialization.

Features
- General Performance Improvements for Throughput
- Improve synchronous request performance with Timers
- Enable C Extensions for PyPy Runtime
- Refactor SerDes functionality for pluggable interface
- Cython SerDes Extension
- Accept iterators/generators for execute_concurrent()
- cythonize existing modules
- Pure Python murmur3 implementation
- Make driver tolerant of inconsistent metadata

Bug Fixes
- Drop Events out-of-order Cause KeyError on Processing
- DowngradingConsistencyRetryPolicy doesn't check response count on write
  timeouts
- Blocking connect does not use connect_timeout
- Properly protect partition key in CQL export
- Trigger error callbacks on timeout

2.6.0

Bug Fixes
- Output proper CQL for compact tables with no clustering columns

2.6.0c2

Features
- Automatic Protocol Version Downgrade
- cqlengine Python 2.6 compatibility
- Double-dollar string quote UDF body
- Set models.DEFAULT_KEYSPACE when calling set_session

Bug Fixes
- Avoid stall while connecting to mixed version cluster
- Make SSL work with AsyncoreConnection in python 2.6.9
- Fix Murmur3Token.from_key() on Windows
- Fix cqlengine TimeUUID rounding error for Windows
- Avoid invalid compaction options in CQL export for non-SizeTiered

2.6.0c1

This release adds support for Cassandra 2.2 features, including
version 4 of the native protocol.

Features
- Default load balancing policy to TokenAware(DCAware)
- Configuration option for connection timeout
- Support User Defined Function and Aggregate metadata in C* 2.2
- Surface request client in QueryTrace for C* 2.2+
- Implement new request failure messages in protocol v4+
- Metadata model now maps index meta by index name
- Support new types in C* 2.2: date, time, smallint, tinyint
- cqle: add Double column type and remove Float overload
- Use partition key column information in prepared response for protocol v4+
- Support message custom payloads in protocol v4+
- Deprecate refresh_schema and replace with functions for specific entities
- Save trace id even when trace complete times out
- Warn when registering client UDT class for protocol < v3
- Support client warnings returned with messages in protocol v4+
- Ability to distinguish between NULL and UNSET values in protocol v4+
- Expose CQL keywords in API

Bug Fixes
- IPv6 address support on Windows
- Convert exceptions during automatic re-preparation to nice exceptions
- cqle: Quote keywords properly in table management functions
- Don't default to GeventConnection when gevent is loaded, but
  not monkey-patched
- Pass dynamic host from SaslAuthProvider to SaslAuthenticator
- Make protocol read_inet work for Windows
- cqle: Correct encoding for nested types
- Update list of CQL keywords used quoting identifiers
- Make ConstantReconnectionPolicy work with infinite retries
- Accept UUIDs with uppercase hex as valid in cqlengine


(fhajny)