[3.0.x] Added documentation extlink for bugs.python.org.

Backport of d02d60eb0f from master

docs/conf.py

@@ -95,6 +95,7 @@ else:
 django_next_version = '3.1'
 
 extlinks = {
+    'bpo': ('https://bugs.python.org/issue%s', 'bpo-'),
     'commit': ('https://github.com/django/django/commit/%s', ''),
     'cve': ('https://nvd.nist.gov/vuln/detail/CVE-%s', 'CVE-'),
     # A file or directory. GitHub redirects from blob to tree if needed.

docs/releases/1.5.1.txt

@@ -10,10 +10,8 @@ compatible with Django 1.5, but includes a handful of fixes.
 The biggest fix is for a memory leak introduced in Django 1.5. Under certain
 circumstances, repeated iteration over querysets could leak memory - sometimes
 quite a bit of it. If you'd like more information, the details are in
-:ticket:`our ticket tracker <19895>` (and in `a related issue`__ in Python
+:ticket:`our ticket tracker <19895>` (and in :bpo:`a related issue <17468>` in
-itself).
+Python itself).
-
-__ https://bugs.python.org/issue17468
 
 If you've noticed memory problems under Django 1.5, upgrading to 1.5.1 should
 fix those issues.

docs/releases/1.6.11.txt

@@ -13,9 +13,9 @@ Last year :func:`~django.utils.html.strip_tags`  was changed to work
 iteratively. The problem is that the size of the input it's processing can
 increase on each iteration which results in an infinite loop in
 ``strip_tags()``. This issue only affects versions of Python that haven't
-received  `a bugfix in HTMLParser <https://bugs.python.org/issue20288>`_; namely
+received :bpo:`a bugfix in HTMLParser <20288>`; namely Python < 2.7.7 and
-Python < 2.7.7 and 3.3.5. Some operating system vendors have also backported
+3.3.5. Some operating system vendors have also backported the fix for the
-the fix for the Python bug into their packages of earlier versions.
+Python bug into their packages of earlier versions.
 
 To remedy this issue, ``strip_tags()`` will now return the original input if
 it detects the length of the string it's processing increases. Remember that

docs/releases/1.7.7.txt

@@ -13,9 +13,9 @@ Last year :func:`~django.utils.html.strip_tags`  was changed to work
 iteratively. The problem is that the size of the input it's processing can
 increase on each iteration which results in an infinite loop in
 ``strip_tags()``. This issue only affects versions of Python that haven't
-received  `a bugfix in HTMLParser <https://bugs.python.org/issue20288>`_; namely
+received :bpo:`a bugfix in HTMLParser <20288>`; namely Python < 2.7.7 and
-Python < 2.7.7 and 3.3.5. Some operating system vendors have also backported
+3.3.5. Some operating system vendors have also backported the fix for the
-the fix for the Python bug into their packages of earlier versions.
+Python bug into their packages of earlier versions.
 
 To remedy this issue, ``strip_tags()`` will now return the original input if
 it detects the length of the string it's processing increases. Remember that