CRM-15097 - CiviCase XML - Parse/encode property "forkable"
CRM-15097 - CaseType - Compute & enforce pseudo-properties, isForkable & isForked
CRM-15097 - crmCaseType - If a case-type isn't forkable, then don't allow editing of its definition.
CRM-15097 - crmCaseType - Allow reverting changes to case-types