bug#4921: Size of cursor and unknown-character boxes

[Per Starbäck]

In GNU Emacs 23.1.1 (i686-pc-linux-gnu, GTK+ Version 2.10.4),
also tested with current cvs emacs:

emacs -q foo

f o o C-u C-u C-x C-+

I get a normal-sized cursor. I expected a mighty cursor on steroids to
got with the large text.

C-o

Now with a newline after point I get a big cursor.

C-x 8 RET mahjong tile red dragon RET C-b

I don't have that character in my fonts. I get a rectangle which is
high as a big character but wide as a normal character,
and a normal-sized cursor. I expected a wider rectangle and cursor.