When changing split windows to diff buffer, title ! updated

[lanurmi]

When changing buffers the title is updated, however, when moving between, say, the top and bottom frame containing two different files, the title is not updated. Therefore, the title may say ABC.txt while your actually editing DEF.txt in the lower window frame.

Reported by: *anonymous

Original Ticket: "efte/bugs/27":https://sourceforge.net/p/efte/bugs/27