VT_100 emulation on SUN 2

[Guy Harris]

> I thing shelltool or cmdtool, if you made them 24 x 80 exactly,
> would emulate VT100 closely enough to work with VMS.

Doubtful.  The terminal emulated by "shelltool" (and by later versions of
"cmdtool" when running in "full-screen" or "Disable Scrolling" mode) is an ANSI
X3.64-compliant terminal, just as a VT100 is; however, both terminals have a
number of "private" escape sequences (for which X3.64 makes provisions) that
are INcompatible.  One such escape sequence is the "set scrolling region"
escape sequence on a VT100, which doesn't exist in "shelltool"; instead, the
same sequence does something quite different (it sets the number of lines by
which the screen scrolls up).  Unfortunate, but true.