Pinning on protobuf==3.0.0a3.

Caused by a breakage in latest protobuf release (3.0.0b1.post1).

Author: dhermes

setup.py

@@ -14,7 +14,7 @@
 REQUIREMENTS = [
     'httplib2 >= 0.9.1',
     'oauth2client >= 1.4.6',
-    'protobuf >= 3.0.0a3',
+    'protobuf == 3.0.0a3',
     'pycrypto',
     'six',
 ]

tox.ini

@@ -10,7 +10,6 @@ commands =
 deps =
     nose
     unittest2
-    protobuf>=3.0.0a3
 setenv =
     PYTHONPATH = {toxinidir}/_testing
 covercmd =
@@ -77,7 +76,6 @@ deps =
     pep8
     pylint
     unittest2
-    protobuf==3.0.0-alpha-1
 passenv = {[testenv:system-tests]passenv}
 
 [testenv:system-tests]