avoid multiple prepares per host with multiple sessions
Merge pull request #150 from aholmberg/1.0

avoid multiple prepares per host with multiple sessions
Fix changelog
Don't crash if replicate_on_write is null on a table

JAVA-254 #fixes
Merge branch '1.0' into 2.0

Conflicts:
	driver-core/CHANGELOG.rst
	driver-core/src/main/java/com/datastax/driver/core/Cluster.java
	driver-core/src/main/java/com/datastax/driver/core/SessionManager.java