Fix a Simultaneous exception when test_reenter.py is run

The test_reenter.py test starts and stops the event loop several
times. The queue_poller is a singleton only created once and, on
the Mac (and probably on FreeBSD) the self.event_map needs to be
reinitialized. While not seen on Linux the same fix is made for
consistency.

coro/linux_poller.pyx

@@ -249,6 +249,7 @@ cdef public class queue_poller [ object queue_poller_object, type queue_poller_t
         if self.ep_fd != -1:
             unistd.close (self.ep_fd)
             self.ep_fd = -1
+        self.event_map = {}
         IF COMPILE_LINUX_AIO:
             aio_teardown()
 

coro/poller.pyx

@@ -298,6 +298,7 @@ cdef public class queue_poller [ object queue_poller_object, type queue_poller_t
         if self.kq_fd != -1:
             unistd.close (self.kq_fd)
             self.kq_fd = -1
+        self.event_map = {}
 
     cdef object set_wait_for (self, kevent_key kk, unsigned int fflags):
         cdef kevent * k