Bug in management of space permissions for a group.

See CSP-1235 for full details.

The stack trace is as follows:

org.springframework.orm.hibernate.HibernateObjectRetrievalFailureException: deleted object would be re-saved by cascade (remove deleted object from associations): 2949, of class: com.atlassian.confluence.security.SpacePermission; nested exception is net.sf.hibernate.ObjectDeletedException: deleted object would be re-saved by cascade (remove deleted object from associations): 2949, of class: com.atlassian.confluence.security.SpacePermission
net.sf.hibernate.ObjectDeletedException: deleted object would be re-saved by cascade (remove deleted object from associations): 2949, of class: com.atlassian.confluence.security.SpacePermission
at net.sf.hibernate.impl.SessionImpl.forceFlush(SessionImpl.java:763)
at net.sf.hibernate.impl.SessionImpl.save(SessionImpl.java:741)