Add tests for new PyErr_NormalizeException() behavior

Add raise_exception() to the _testcapi module.  It isn't a test, but
the C API exists only to support test_exceptions.  raise_exception()
takes two arguments -- an exception class and an integer specifying
how many arguments it should be called with.

test_exceptions uses BadException() to test the interpreter's behavior
when there is a problem instantiating the exception.  test_capi1()
calls it with too many arguments.  test_capi2() causes an exception to
be raised in the Python code of the constructor.

Lib/test/test_exceptions.py

@@ -3,6 +3,8 @@
 from test_support import *
 from types import ClassType
 import warnings
+import sys, traceback
+import _testcapi
 
 warnings.filterwarnings("error", "", OverflowWarning, __name__)
 
@@ -161,4 +163,37 @@ r(Exception)
 try: x = 1/0
 except Exception, e: pass
 
+# test that setting an exception at the C level works even if the
+# exception object can't be constructed.
+
+class BadException:
+    def __init__(self):
+        raise RuntimeError, "can't instantiate BadException"
+
+def test_capi1():
+    try:
+        _testcapi.raise_exception(BadException, 1)
+    except TypeError, err:
+        exc, err, tb = sys.exc_info()
+        co = tb.tb_frame.f_code
+        assert co.co_name == "test_capi1"
+        assert co.co_filename.endswith('test_exceptions.py')
+    else:
+        print "Expected exception"
+test_capi1()
+
+def test_capi2():
+    try:
+        _testcapi.raise_exception(BadException, 0)
+    except RuntimeError, err:
+        exc, err, tb = sys.exc_info()
+        co = tb.tb_frame.f_code
+        assert co.co_name == "__init__"
+        assert co.co_filename.endswith('test_exceptions.py')
+        co2 = tb.tb_frame.f_back.f_code
+        assert co2.co_name == "test_capi2"
+    else:
+        print "Expected exception"
+test_capi2()
+
 unlink(TESTFN)