Kill several problems at once: test_poll() failed sometimes for me.

Turns out the mysterious "expected output" file contained exactly N dots,
because test_poll() has a loop that *usually* went around N times,
printing one dot on each loop trip.  But there's no guarantee of that,
because the exact value of N depended on the vagaries of scheduling
time.sleep()s across two different processes.  So stopped printing dots,
and got rid of the expected output file.  Add a loop counter instead,
and verify that the loop goes around at least a couple of times.  Also
cut the minimum time needed for this test from 4 seconds to 1.

Lib/test/output/test_subprocess

@@ -1,2 +0,0 @@
-test_subprocess
-.........

Lib/test/test_subprocess.py

@@ -350,11 +350,16 @@ class ProcessTestCase(unittest.TestCase):
 
     def test_poll(self):
         p = subprocess.Popen([sys.executable,
-                          "-c", "import time; time.sleep(4)"])
-        while p.poll() == None:
-            sys.stdout.write(".")
-            sys.stdout.flush()
-            time.sleep(0.5)
+                          "-c", "import time; time.sleep(1)"])
+        count = 0
+        while p.poll() is None:
+            time.sleep(0.1)
+            count += 1
+        # We expect that the poll loop probably went around about 10 times,
+        # but, based on system scheduling we can't control, it's possible
+        # poll() never returned None.  It "should be" very rare that it
+        # didn't go around at least twice.
+        self.assert_(count >= 2)
         # Subsequent invocations should just return the returncode
         self.assertEqual(p.poll(), 0)