Browsing Lithuanian translation

When the user eventually pushes the OK button, BFU calls
* bookmark_add_add() and gives it the struct dialog * as the
* void * parameter.  However, bookmark_add_add() also needs
* to know the struct terminal *, and there is no way to get
* that from struct dialog.  The other bookmark dialogs work
* around that by making dialog.udata point to the struct
* dialog_data of the bookmark manager, but the "Add bookmark"
* dialog can be triggered with ACT_MAIN_ADD_BOOKMARK, which
* does not involve the bookmark manager at all.
*
* The solution here is to save the struct terminal * in
* dialog.udata2, which the "Edit bookmark" dialog uses for
* struct bookmark *.  When adding a new bookmark, we don't
* need a pointer to an existing one, of course.