Tweaks to newly-declared NSString * constants to make them usable from clients

        * Storage/WebDatabaseManagerPrivate.h:
        * Storage/WebDatabaseManager.mm:
        removed "const" from new NSNotification names and userInfo keys; these generate compiler warnings when used
        
        * WebKit.exp:
        export new NSNotification names and userInfo keys so clients can use them



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@28245 268f45cc-cd09-0410-ab3c-d52691b4dbfc