GIRAPH-704: Specialized message stores (majakabiljo)
GIRAPH-705: Type converters and giraph-hive cleanup (nitay)
Merge remote-tracking branch 'origin/trunk' into factories

Conflicts:
	giraph-core/src/main/java/org/apache/giraph/comm/ServerData.java
	giraph-core/src/main/java/org/apache/giraph/comm/messages/InMemoryMessageStoreFactory.java