Add prepared stmnt cases to type tests
Handle tracing flags on encode/decode
Use logging for decoder warnings
Merge branch 'master' into tracing-support

Conflicts:
	cassandra/decoder.py
First draft of QueryTrace, TraceEvent classes
Fix bad trace body read, convert to UUID
Add __str__ for trace classes, friendlier types
Enable tracing through execute(_async)() kwarg only
Documentation for new tracing classes and attrs
Add method to retrieve query trace
Remove tracing from TODO list in README
Correct callback erroring when message can't be decoded
Add some missing tracing documentation
Use internal OrderedDict class if not found in collection (python <2.7 users)
Merge pull request #3 from daubman/ordered_dict_pre27_fix

Use internal OrderedDict class if not found in collection
Specify full package and module on imports
Use internal WeakSet if unable to import (users of Python < 2.7)
Merge pull request #4 from daubman/use_internal_weakset_if_missing

Use internal WeakSet if unable to import (users of Python < 2.7)
Tolerate unknown host DCs more gracefully

For load balancing purposes, hosts are assumed to be in
the local datacenter now if the actual datacenter is unknown.

However, this is still a slight problem with contact points
in a remote DC when using DCAwareRoundRobinPolicy. See
https://datastax-oss.atlassian.net/browse/JAVA-138 for
more details.

Fixes #5
import from concurrent.futures rather than futures to prevent annoying DeprecationWarning