WebHistoryItem now supports getting and setting arbitrary properties via _transientPropertyForKey: and
        -_setTransientProperty:forKey:.
        For now, these properties do not persist with the rest of the history data.  They are intended to hold transient
        per-history-item state, which is something that was until now difficult for a WebKit client app to do.
        
        * History/WebHistoryItemPrivate.h:
        * History/WebHistoryItem.m:
        (-[WebHistoryItemPrivate dealloc]):
        (-[WebHistoryItem _transientPropertyForKey:]):
        (-[WebHistoryItem _setTransientProperty:forKey:]):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@15094 268f45cc-cd09-0410-ab3c-d52691b4dbfc