Notebook needs to underscore-escape tab titles for context menu

[gue5t gue5t]

To reproduce, run "midori -p http://foo_bar/ http://baz__qux/", and then right-click empty space in the tab bar and look at the items in the list for the two open tabs. Notice that the first underscore in each has been converted to an accelerator underline. I'm not yet sure whether this occurs under granite.

This should be fixed in midori_browser_notebook_button_press_event_after_cb around midori-browser.c:5277.