window-height documentation doesn't mention header-line-format

[Allograph Petrofsky]

In emacs 21.1,

The doc string for window-height and the info node "(elisp) Size of
Window" fail to mention that the header line is included in the return
value.

It seems there should be a window-body-height function that returns
the window height minus zero, one, or two, according to the value of
mode-line-format and header-line-format in the buffer that the window
displays.  I imagine there are many instances of (1- (window-height))
that need to be changed to calls to window-body-height.

-al