fix compilation warnings

gevent/callbacks.c

@@ -160,7 +160,7 @@ static void gevent_call(struct PyGeventLoopObject* loop, struct PyGeventCallback
         Py_DECREF(result);
     }
     else {
-        gevent_handle_error(loop, cb);
+        gevent_handle_error(loop, (PyObject*)cb);
     }
 
     Py_INCREF(Py_None);

gevent/core.ppyx

@@ -30,7 +30,7 @@ cdef extern from "callbacks.h":
     void gevent_callback_stat(libev.ev_loop, void*, int)
     void gevent_run_callbacks(libev.ev_loop, void*, int)
     void gevent_periodic_signal_check(libev.ev_loop, void*, int)
-    void gevent_call(object, object)
+    void gevent_call(loop, callback)
 
 cdef extern from *:
     int errno