acme: increase timer resolution to 10ms

We ran for a long time with 10ms kernel resolution,
so 10ms user space resolution here should be fine.
Some systems actually provide 1ms sleeps, which
makes this polling use a bit more cpu than we'd like.
Since the timers are for user-visible things, 10ms should
still be far from noticeable.

Reduces acme's cpu usage on Macs when plumber is missing
(and plumbproc is sleeping waiting for it to appear).

LGTM=aram, r
R=r, aram
https://codereview.appspot.com/99570043

src/cmd/acme/time.c

@@ -50,7 +50,7 @@ timerproc(void *v)
 	nt = 0;
 	old = msec();
 	for(;;){
-		sleep(1);	/* will sleep minimum incr */
+		sleep(10);	/* longer sleeps here delay recv on ctimer, but 10ms should not be noticeable */
 		new = msec();
 		dt = new-old;
 		old = new;