top: immunize against window manager flood of SIGWINCH

Whew, it was nip-and-tuck there for awhile but finally
we solved the SIGWINCH overload problem one finds with
most X window managers. Now if a window manager should
try to inundate ol' top with repeated SIGWINCH signals
they won't even be received so can't impact us at all.

And we achieve this miracle having never even issued a
sigprocmask, so all the top code executes with signals
totally unblocked. Intuition suggests it probably rubs
even more salt in the wound, but au contraire mon ami!

The key to our success was simply trading the 'select'
call for its cousin 'pselect'. Not only does that call
provide nanosecond granularity (vs. the former's usec)
but it takes a sigset_t parm which can then atomically
block the troublesome SIGWINCH guy until user input or
optional timeout. Net result? No more signal overload!

Now, if only we could just coax all terminal emulators
into one identical standard buffering scheme plus find
some way to emulate the most recent SIGWINCH, it would
be perfect. We would then obviate the user requirement
of typing yet 1 more key before seeing proper results.

(everything is perfectly justified plus right margins)
(are completely filled, but of course it must be luck)

Reference(s):
http://www.freelists.org/post/procps/unwanted-topinspect-window-enclosure-with-the-terminal-size-change
http://www.freelists.org/post/procps/Sourceforge-project,7

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

top/top.h

@@ -630,7 +630,7 @@ typedef struct WIN_t {
 /*------  Low Level Memory/Keyboard/File I/O support  --------------------*/
 //atic void         *alloc_c (size_t num);
 //atic void         *alloc_r (void *ptr, size_t num);
-//atic inline int    ioa (struct timeval *tv);
+//atic inline int    ioa (struct timespec *ts);
 //atic int           ioch (int ech, char *buf, unsigned cnt);
 //atic int           iokey (int init);
 //atic char         *ioline (const char *prompt);