bpo-28958: Improve SSLContext error reporting. (#3414)

Signed-off-by: Christian Heimes <christian@python.org>

Misc/NEWS.d/next/Library/2017-09-06-19-41-01.bpo-28958.x4-K5F.rst

@@ -0,0 +1,2 @@
+ssl.SSLContext() now uses OpenSSL error information when a context cannot be
+instantiated.

Modules/_ssl.c

@@ -2636,8 +2636,7 @@ _ssl__SSLContext_impl(PyTypeObject *type, int proto_version)
         return NULL;
     }
     if (ctx == NULL) {
-        PyErr_SetString(PySSLErrorObject,
-                        "failed to allocate SSL context");
+        _setSSLError(NULL, 0, __FILE__, __LINE__);
         return NULL;
     }