gnu: python: Fix CVE-2018-14647.

* gnu/packages/patches/python-CVE-2018-14647.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/python.scm (python-3/fixed): New variable.
(python-3.6)[replacement]: New field.
(python-minimal, python-debug, wrap-python3): Use PACKAGE/INHERIT instead of
standard inheritance.

gnu/packages/patches/python-CVE-2018-14647.patch

@@ -0,0 +1,61 @@
+Fix CVE-2018-14647:
+https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-14647
+https://bugs.python.org/issue34623
+
+Taken from upstream:
+https://github.com/python/cpython/commit/f7666e828cc3d5873136473ea36ba2013d624fa1
+
+diff --git Include/pyexpat.h Include/pyexpat.h
+index 44259bf6d7..07020b5dc9 100644
+--- Include/pyexpat.h
++++ Include/pyexpat.h
+@@ -3,7 +3,7 @@
+ 
+ /* note: you must import expat.h before importing this module! */
+ 
+-#define PyExpat_CAPI_MAGIC  "pyexpat.expat_CAPI 1.0"
++#define PyExpat_CAPI_MAGIC  "pyexpat.expat_CAPI 1.1"
+ #define PyExpat_CAPSULE_NAME "pyexpat.expat_CAPI"
+ 
+ struct PyExpat_CAPI
+@@ -48,6 +48,8 @@ struct PyExpat_CAPI
+     enum XML_Status (*SetEncoding)(XML_Parser parser, const XML_Char *encoding);
+     int (*DefaultUnknownEncodingHandler)(
+         void *encodingHandlerData, const XML_Char *name, XML_Encoding *info);
++    /* might be none for expat < 2.1.0 */
++    int (*SetHashSalt)(XML_Parser parser, unsigned long hash_salt);
+     /* always add new stuff to the end! */
+ };
+ 
+diff --git Modules/_elementtree.c Modules/_elementtree.c
+index 707ab2912b..53f05f937f 100644
+--- Modules/_elementtree.c
++++ Modules/_elementtree.c
+@@ -3261,6 +3261,11 @@ _elementtree_XMLParser___init___impl(XMLParserObject *self, PyObject *html,
+         PyErr_NoMemory();
+         return -1;
+     }
++    /* expat < 2.1.0 has no XML_SetHashSalt() */
++    if (EXPAT(SetHashSalt) != NULL) {
++        EXPAT(SetHashSalt)(self->parser,
++                           (unsigned long)_Py_HashSecret.expat.hashsalt);
++    }
+ 
+     if (target) {
+         Py_INCREF(target);
+diff --git Modules/pyexpat.c Modules/pyexpat.c
+index 47c3e86c20..aa21d93c11 100644
+--- Modules/pyexpat.c
++++ Modules/pyexpat.c
+@@ -1887,6 +1887,11 @@ MODULE_INITFUNC(void)
+     capi.SetStartDoctypeDeclHandler = XML_SetStartDoctypeDeclHandler;
+     capi.SetEncoding = XML_SetEncoding;
+     capi.DefaultUnknownEncodingHandler = PyUnknownEncodingHandler;
++#if XML_COMBINED_VERSION >= 20100
++    capi.SetHashSalt = XML_SetHashSalt;
++#else
++    capi.SetHashSalt = NULL;
++#endif
+ 
+     /* export using capsule */
+     capi_object = PyCapsule_New(&capi, PyExpat_CAPSULE_NAME, NULL);