Update documentation around time.Sleep to specify its precision, and suggest

a possible interface for more granular sleep times.

Fixes issue #260.

R=rsc, r
CC=golang-dev
https://golang.org/cl/181058

src/pkg/time/sleep.go

@@ -9,6 +9,7 @@ import (
 	"syscall"
 )
 
-// Sleep pauses the current goroutine for ns nanoseconds.
-// It returns os.EINTR if interrupted.
+// Sleep pauses the current goroutine for at least ns nanoseconds. Higher resolution
+// sleeping may be provided by syscall.Nanosleep on some operating systems.
+// Sleep returns os.EINTR if interrupted.
 func Sleep(ns int64) os.Error { return os.NewSyscallError("sleep", syscall.Sleep(ns)) }