fix unit test
add taskMemory for RDD.uniq()
bugfix
fallback to client in pure Python when no native available

The Mesos Client in pure python is compatible with Mesos 0.9,
which can work with PyPy, is dependent on kazoo (ZooKeeper client in Python)
update setup.py to include dpark.pymesos
add dependence of msgpack-python and protobuf
auto detect virtual environment and switch to it
Merge branch 'master' into release