Stackless issue python#265: fix PyChannel_Send_M

The implementation was buggy. This affects only users of the C-API,
that call PyChannel_Send() and PyChannel_Send_nr() for calls from
outside of the interpreter (with no main-tasklet).

Stackless/changelog.txt

@@ -9,6 +9,10 @@ What's New in Stackless 3.X.X?
 
 *Release date: 20XX-XX-XX*
 
+- https://github.com/stackless-dev/stackless/issues/265
+  Fix C-API functions PyChannel_Send() and PyChannel_Send_nr() for calls from
+  outside of the interpreter (with no main-tasklet).
+
 - https://github.com/stackless-dev/stackless/issues/264
   Implement bpo-35134 for Stackless: move header Include/slp_tstate.h to
   Include/cpython/slp_tstate.h.

Stackless/module/channelobject.c

@@ -425,10 +425,13 @@ the sender will be blocked. Otherwise, the receiver will\n\
 be activated immediately, and the sender is put at the end of\n\
 the runnables list.");
 
+static PyObject *
+impl_channel_send(PyChannelObject *self, PyObject *arg);
+
 static PyObject *
 PyChannel_Send_M(PyChannelObject *self, PyObject *arg)
 {
-    PyMethodDef def = {"send", (PyCFunction)PyChannel_Send, METH_O};
+    PyMethodDef def = {"send", (PyCFunction)impl_channel_send, METH_O};
     return PyStackless_CallCMethod_Main(&def, (PyObject *) self, "O", arg);
 }