I have removed the reST target I added in 38cdca2cc253: it is not necessary, as
people can link to the glossary entry or the abc module without it.
Two indentation fixes from 3.2 collections.rst have been ported to 3.3
collections.abc.rst.
The previous markup hijacked the abstract-base-classes glossary entry,
which resulted in the HTML linking to collections.abc when defining the
generic ABC concept. Now the glossary links to the abc module.
called collections.abc, following the pattern used by importlib.abc. For
backwards compatibility, the names continue to also be imported into the
collections module.