doc/common.txt

filter: `updatebranchcache` during `addchangegroup` instead of after lock

The forced recomputation of the branch cache was introduced by `ee317dbfb9d0`.
Back there, `addchangegroup` did not handle any lock logic.

Later `ee1ed6afac21` introduced lock logic to `addchangegroup`. Its description
does not explain why the `updatebranchcache` call is made outside locking. I
believe that the lock was released there because it fit well with the transaction
release already in the code.

Finally `926a06f7a353` moved all "unlocked" code of `addchangegroup` to an
`repo._afterlock` callback.

I do not think that the call to `updatebranchcache()` requires to be done
outside locking. That may even be a bad idea to do so. Bringing this call back
in the `addchangegroup` function makes the flow simpler and eases the following
up changelog level filtering business.

.. Common link and substitution definitions.

.. |hg(1)| replace:: **hg**\ (1)
.. _hg(1): hg.1.html
.. |hgrc(5)| replace:: **hgrc**\ (5)
.. _hgrc(5): hgrc.5.html
.. |hgignore(5)| replace:: **hgignore**\ (5)
.. _hgignore(5): hgignore.5.html