top: introduced new focus toggle ('F'), program source

top: introduced new focus toggle ('F'), program source

Sometimes, it might be useful to isolate a parent task
and its forked children from other system activity. As
an example, a user might want to examine workload in a
specific lxc container. Or maybe there is some need to
question what's happening under the same tmux session.

Since forest view mode tends to be a relatively stable
display, it will sometimes satisfy the above need. But
that mode can't currently guarantee the target process
always remains as the topmost task or even is visible.

So, this patch will enable focusing on any parent task
and keeping it as the topmost process while displaying
it and its forked children only. It then appears as if
there is no other activity in that system by virtue of
the blank lines which follow that final child process.

To implement this new feature, top's redundant 'F' key
has been repurposed. It made little sense devoting two
keys to the Fields Management screen (especially since
the key we've taken required two separate keystrokes).

[ and while we're at it, i also added punctuation to ]
[ the prologue for that renamed 'forest_display' guy ]
[ since all other forest functions used punctuation. ]

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