TIMER: Compiler warnings, Windows Sleep()

- Reduce/eliminate compiler warnings
    - Variables that hide previous definitions (e.g., uptr)
    - Assignments in conditional expressions (conditional expressions
      should be... conditionals, i.e. "==".)

- Readability: use constants for conversions, make it easier to see the
  time units.

- Use size_t for array indices.

- Windows: Prefer waitable timers over Sleep(). Sleep() is the fallback
  if initializing a waitable timer fails (which it doesn't, but there's
  no penalty for writing safe code.) A detailed discussion on Windows
  timers can be found at http://www.windowstimestamp.com/description

  Significantly reduces the occasional headache-inducing slow redraw
  (flicker) on Windows (Imlac, primarily, but also afflicts PDP11 VT
  sometimes.)

Author: bscottm

sim_console.c

@@ -204,7 +204,7 @@ t_bool sim_signaled_int_char                            /* WRU character detecte
 #else
                              = TRUE;
 #endif
-uint32 sim_last_poll_kbd_time;                          /* time when sim_poll_kbd was called */
+uint32 sim_last_poll_kbd_time = 0;                      /* time when sim_poll_kbd was called */
 extern TMLN *sim_oline;                                 /* global output socket */
 static uint32 sim_con_pos;                              /* console character output count */