v2.9.1 release

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v2.8.1 release

v2.8.0 release

v2.7.1 release

v2.7.0 release

Fixing another `git rebase master` accident.

Merge branch 'test_unique_ptr_member' into pr2672_use_smart_holder_as…

…_default

Adding source code comments in response to review.

Manipulating failing ConstructorStats test to pass, to be able to run…

… all tests with ASAN.

This version of the code is ASAN clean with unique_ptr or smart_holder as the default.

This change needs to be reverted after adopting the existing move-only-if-refcount-is-1
logic used by type_caster_base.