MFC r253118: Fix conditional (der should match the comment above it).

MFC r253118: Fix conditional (der should match the comment above it).
MFC r253117:

Do two things: First, don't obscure the backtitle. Second, read ~/.dialogrc
if it exists to determine if use_shadow is true (ON) or false (OFF).

The purpose of determining the value of use_shadow is to know how many lines
to subtract from the maximum height value in assuring that the backtitle is
not obscured.

The detriment of obscuring the backtitle is that it provides information
that is not easily obtained elsewhere. That is the command-line shortcut
used to access the current menu. As you navigate from one dialog to the
next, invariably transparently corssing module boundaries, the backtitle
represents the command-line argument used to get there. Obscuring this
information with a widget that is too-tall and/or too-wide would see that
data go unnoticed (leaving few other ways to get that information in the
same helpful context).

So despite the fact that this change reduces the standard maximum height for
all widgets, there is a trap-door to prevent this calculation. If you want
to utilize the full screen height on the terminal (remember, this adjustment
is not made for Xdialog(1)) you can set $NO_BACKTITLE to 1 (or any non-NULL
value for that matter) and this calculation will be skipped. You will be
able to draw a widget that partially obscures the backtitle if-necessary.

git-svn-id: svn://svn.freebsd.org/base/stable/9@253169 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f