Fix a bug in our win32 condition implementation

The do ... while loop in our wait code could spin while waiting
because the event object wasn't reset until there were no longer any
events waiting to be woken up.  We also want to reset the event object
if the count of events to wake up reaches zero.

Found by Chris Davis.  Fixes bug 3053358.

evthread_win32.c

@@ -253,20 +253,30 @@ evthread_win32_cond_wait(void *_cond, void *_lock, const struct timeval *tv)
 			--cond->n_waiting;
 			result = 0;
 			waiting = 0;
+			goto out;
 		} else if (res != WAIT_OBJECT_0) {
 			result = (res==WAIT_TIMEOUT) ? 1 : -1;
 			--cond->n_waiting;
 			waiting = 0;
+			goto out;
 		} else if (ms != INFINITE) {
 			endTime = GetTickCount();
 			if (startTime + ms_orig <= endTime) {
 				result = 1; /* Timeout */
 				--cond->n_waiting;
 				waiting = 0;
+				goto out;
 			} else {
 				ms = startTime + ms_orig - endTime;
 			}
 		}
+		/* If we make it here, we are still waiting. */
+		if (cond->n_to_wake == 0) {
+			/* There is nobody else who should wake up; reset
+			 * the event. */
+			ResetEvent(cond->event);
+		}
+	out:
 		LeaveCriticalSection(&cond->lock);
 	} while (waiting);