KahaDB, Doc ; checksumJournalFiles in 6.1 doc should have default of "true"

I think the docs need updating. In [1] the default value for checksumJournalFiles is doc'd as false. In ActiveMQ 5.9 (A-MQ 6.1) default value was changed to true.

[1]https://access.redhat.com/documentation/en-US/Red_Hat_JBoss_A-MQ/6.1/html/Configuring_Broker_Persistence/KahaDBConfiguration.html