Fix python package version to alpha-2.

Change-Id: Iae16dcae833959681a5c8e98764e5d1071e6fdcf

python/google/protobuf/__init__.py

diff --git a/python/google/protobuf/__init__.py b/python/google/protobuf/__init__.py
index ec3b093..d1af74b 100755
--- a/python/google/protobuf/__init__.py
+++ b/python/google/protobuf/__init__.py
@@ -32,4 +32,4 @@
 #
 # Copyright 2007 Google Inc. All Rights Reserved.
 
-__version__ = '3.0.0-pre'
+__version__ = '3.0.0-alpha-2'