top: extend 'focus' navigation to shift+tab (back_tab)
Some of those bottom windows grow quite large, as with
the firefox environment. If one is navigating the data
using the tab key, it can be very inconvenient when an
element should be reexamined but that focus has moved.
Therefore, this commit will support the 'back_tab' key
which is a standard combination of the shift+tab keys.
Now a user can easily backup up to any missed element,
assuming a terminal emulator honors that terminfo key.
[ a gui emulator typically will honor the 'back_tab' ]
[ terminfo string, whereas a linux console does not. ]
Signed-off-by: Jim Warner <james.warner@comcast.net>