I didn't realize this was waiting for me.  You should have just checked
it in, that would have gotten me to review faster. :-)

pythonrun.c:
 * Should PyModule_GetWarningsModule() return a valid pointer?
 * The code below crashes.  Need to XDECREF, not DECREF (or similar).
+        PyObject *warnings_module = PyImport_ImportModule("warnings");
+        if (!warnings_module)
+            PyErr_Clear();
+        Py_DECREF(warnings_module);

Python/_warnings.c:
 * Remove // XXX(nnorwitz): need to parse -W cmd line flags

Include/pythonrun.h
 * init_warnings has the wrong name (not prefixed with _Py).  I'm not
sure it should be exported at all.

test_support/frozen:  did you want the captured_std{out,err} change in
this patch?

Changes to Makefile.pre.in other than adding _warnings.o?

I think this is good enough if it's working.  How about checking it in
after 1) the alpha is released Wed and 2) fixing up the nits?