bug#7390: 24.0.50; pos-col-row gives incorrect row

[Drew Adams]

> As a matter of fact, this problem is present in Emacs 23.2 as well,
> and in the current pretest of Emacs 23.3.
> 
> An easier way to reproduce is this:
> 
>   emacs -Q
>   C-x b foo RET
>   M-: (setq header-line-format "foo") RET
>   M-x picture-mode RET
> 
> Now type 2 lines of text, and click the mouse on the first line.

Thanks for narrowing this down, in particular removing tabbar.el from the
equation.