alarm_signal_handler is called too frequently

[YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>]

I noticed that alarm_signal_handler was called too frequently on the
system that used polling with SIGALRM (such as Solaris/X11 and Mac OS
X/Carbon).  In alarm_signal_handler, set_alarm is called even when
interrupt_input_blocked is non-zero where no timer function is
executed.  If BLOCK_INPUT continues for a long time, which is typical
in Mac OS X/Carbon, set_alarm will set the timer value to 1000 usec
because the current time (now) exceeds the old expiration time
(atimers->expiration).  I think we don't have to call set_alarm when
pending_atimers is non-zero because do_pending_atimers is supposed to
be called eventually in such a case.  Is that correct?

The following patch also apparently reduces the CPU usage during the
idle time (~1.0% -> 0.0% on my PowerBook G4 667MHz).

				     YAMAMOTO Mitsuharu
				mituharu@math.s.chiba-u.ac.jp

Index: src/atimer.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/atimer.c,v
retrieving revision 1.16
diff -c -r1.16 atimer.c
*** src/atimer.c	19 Jul 2004 04:42:43 -0000	1.16
--- src/atimer.c	13 Oct 2004 00:56:47 -0000
***************
*** 397,403 ****
        EMACS_GET_TIME (now);
      }
  
!   set_alarm ();
  }
  
  
--- 397,404 ----
        EMACS_GET_TIME (now);
      }
  
!   if (!pending_atimers)
!     set_alarm ();
  }