[Image-SIG] [BUG] [PIL 1.1.17] Image.show() on unix displays image twice if xv and display are installed

[solsTiCe d'Hiver]

hello,
I was using the .show() function on an Image object, and I had the
surprise to see 2 windows poping-up on my screen. One is xv and the
other one is display.

There is a little bug in ImageShow.py because the Viewer.show() is a
procedure and does not return anything. 
Well, in fact, it returns None which is interpreted as False. Hence the
bug.

cheers