top: avoid any potential race involving 'BREAK_screen'

top: avoid any potential race involving 'BREAK_screen'

When that 'Bottom' window was being finalized, an enum
of BREAK_screen was added to the Frames_signal values.
This was done so some full screen replacement function
could flag the need for that bottom window to go away.

Around that same time, top was made more responsive to
keyboard input so that residual portions of a previous
bottom window would not linger until the next refresh.
This happened if going from a larger (^N, environment)
bottom window to some smaller window (^P, namespaces).

The combined effect of these changes was to create the
potential race condition this commit addresses. If the
user encountered a SIGWINCH while on any of those full
screen replacement displays (help, fields mgmt, etc.),
endless redraws would occur. A ^C was the only option.

Henceforth we will protect against any redraw loops by
clearing Frames_signal each time a redraw is required.

[ along the way, we'll make the 'q' key work on that ]
t secondary 'windows' help screen as it should, even ]
[ though it is not documented on that screen itself. ]

Reference(s):
. May, 2022 - more responsive to keyboard input
commit 3ea1bc779fb7ca5bf065a5ca620ec5b5823bc61c
. May, 2022 - maybe force the bottom window off
commit d66c1f39b52d53ec279fc638aa4a6352d7672201

Signed-off-by: Jim Warner <james.warner@comcast.net>