Checked the following locations:

 * Model.save(): If there are parents involved, take the safe way and use
   transactions since this should be an all or nothing operation.

   If the model has no parents:

    * Signals are executed before and after the previous existing
      transaction -- they were never been part of the transaction.

    * if `force_insert` is set then only one query is executed -> atomic
      by definition and no transaction needed.

    * same applies to `force_update`.

    * If a primary key is set and no `force_*` is set Django will try an
      UPDATE and if that returns zero rows it tries an INSERT. The first
      case is completly save (single query). In the second case a
      transaction should not produce different results since the update
      query is basically a no-op then (might miss something though).

 * QuerySet.update(): no signals issued, single query -> no transaction
   needed.

 * Model/Collector.delete(): This one is fun due to the fact that is
   does many things at once.

   Most importantly though: It does send signals as part of the
   transaction, so for maximum backwards compatibility we need to be
   conservative.

   To ensure maximum compatibility the transaction here is removed only
   if the following holds true:

     * A single instance is being deleted.
     * There are no signal handlers attached to that instance.
     * There are no deletions/updates to cascade.
     * There are no parents which also need deletion.

Follow up to 081e7871.

Fixed #29725 -- Removed unnecessary join in QuerySet.count() and exists() on a many-to-many relation.

The HTML characters are unused because urlize is meant to be applied to
plain text and these characters aren't properly detected (refs #29826).
Angle brackets and quotes are present in word_split_re and therefore
won't be used in WRAPPING_PUNCTUATION.

django.utils.http.urlsafe_base64_encode() now returns a string, not a
bytestring. Since URLs are represented as strings,
urlsafe_base64_encode() should return a string. All uses immediately
decoded the bytestring to a string anyway.

As the inverse operation, urlsafe_base64_decode() accepts a string.

When using include() without namespaces of some urlpatterns that
have an include() with namespace, the converters of the parent
include() weren't being used to convert the arguments of reverse().

Support for passing bytestrings to the database API was removed in
301de774.

contrib.sites is included in INSTALLED_APPS by SitemapTestsBase.

SessionBase.decode() is the inverse operation to SessionBase.encode().
As SessionBase.encode() always returns a string, SessionBase.decode()
should always be passed a string argument. Fixed the file backend, which
was the only backend still passing a bytestring.

The mysqlclient cursor attribute `_last_executed` is always stored as
bytes. Decode it.

TextField values are already type str. No need to decode.