Issue #10278: Drop time.monotonic() function, rename time.wallclock() to time.steady()

 * On Mac OS X, time.steady() now uses mach_absolute_time(), a monotonic clock
 * Optimistic change: bet that CLOCK_MONOTONIC and CLOCK_REALTIME are available
   when clock_gettime() is available
 * Rewrite time.steady() documentation
diff --git a/Lib/test/test_time.py b/Lib/test/test_time.py
index 1fc46aa..2baf066 100644
--- a/Lib/test/test_time.py
+++ b/Lib/test/test_time.py
@@ -331,29 +331,10 @@
             pass
         self.assertEqual(time.strftime('%Z', tt), tzname)
 
-    @unittest.skipUnless(hasattr(time, 'monotonic'),
-                         'need time.monotonic()')
-    def test_monotonic(self):
-        t1 = time.monotonic()
-        t2 = time.monotonic()
-        self.assertGreaterEqual(t2, t1)
-
-        t1 = time.monotonic()
+    def test_steady(self):
+        t1 = time.steady()
         time.sleep(0.1)
-        t2 = time.monotonic()
-        dt = t2 - t1
-        self.assertGreater(t2, t1)
-        self.assertAlmostEqual(dt, 0.1, delta=0.2)
-
-    def test_wallclock(self):
-        t1 = time.wallclock()
-        t2 = time.wallclock()
-        # may fail if the system clock was changed
-        self.assertGreaterEqual(t2, t1)
-
-        t1 = time.wallclock()
-        time.sleep(0.1)
-        t2 = time.wallclock()
+        t2 = time.steady()
         dt = t2 - t1
         # may fail if the system clock was changed
         self.assertGreater(t2, t1)