fix reraise on py3

based on #362 by @fantix

gevent/_util_py2.py

+# this produces syntax error on Python3
+
+
+__all__ = ['reraise']
+
+
+def reraise(type, value, tb):
+    raise type, value, tb

gevent/hub.py

@@ -34,11 +34,19 @@ if PY3:
     string_types = str,
     integer_types = int,
     xrange = range
+
+    def reraise(tp, value, tb=None):
+        if value.__traceback__ is not tb:
+            raise value.with_traceback(tb)
+        raise value
+
 else:
     string_types = basestring,
     integer_types = (int, long)
     xrange = xrange
 
+    from gevent._util_py2 import reraise
+
 
 if sys.version_info[0] <= 2:
     import thread

gevent/pywsgi.py

@@ -11,8 +11,7 @@ from urllib import unquote
 from gevent import socket
 import gevent
 from gevent.server import StreamServer
-from gevent.hub import GreenletExit
-from gevent.hub import PY3
+from gevent.hub import GreenletExit, PY3, reraise
 
 
 __all__ = ['WSGIHandler', 'WSGIServer']
@@ -434,7 +433,7 @@ class WSGIHandler(object):
             try:
                 if self.headers_sent:
                     # Re-raise original exception if headers sent
-                    raise exc_info[0], exc_info[1], exc_info[2]
+                    reraise(*exc_info)
             finally:
                 # Avoid dangling circular ref
                 exc_info = None

util/pyflakes.py

@@ -13,6 +13,7 @@ gevent/__init__.py:\d+:.*imported but unused
 gevent/__init__.py:\d+: redefinition of unused 'signal' from line
 gevent/coros.py:\d+: 'from gevent.lock import *' used; unable to detect undefined names
 gevent/coros.py:\d+: '__all__' imported but unused
+gevent/hub.py:\d+: 'reraise' imported but unused
 gevent/thread.py:\d+: '_local' imported but unused
 gevent/threading.py:\d+: '\w+' imported but unused
 gevent/wsgi.py:1: 'from gevent.pywsgi import *' used; unable to detect undefined names