Jump to Page throws javascript exceptions if the target is not a full wiki page name, i.e. Space.Page

To reproduce:
1. Open the GoToPage dialog (CTRL+G)
2. Open the Firebug console
3. Type in "Space" and press Enter
4. See the exception

To inform the user of the problem (instead of throwing exceptions in the error console), an error notification can be displayed notifying the user that the target reference/page fullName is not complete.