Cursor change on loss of focus

[william.m.miller@gmail.com]

I'm using Emacs 21.3.50.1 under Cygwin/X.  If I have more
than one Emacs window open (within a single X window) and
move the focus from one to the other, the one that has focus
has a blinking block cursor and the one without focus has an
empty block cursor.

Is there a way to turn the blinking block cursor into an
empty block cursor when I move the focus to a different
X window (i.e., a different, non-Emacs application)?  I
can't count the number of times I've started typing Emacs
keystrokes to other programs, intending to work with the
text in my Emacs window, and I think it's because I
subconsciously key on the blinking block cursor to
recognize which window is going to receive my keystrokes,
rather than looking at the color of the window's title bar.

Any suggestions would be appreciated.