[docs] Glossary entry for __future__ module contradicts module's documentation

[Alexander Belopolsky]

Compare:

__future__: A *pseudo-module* which programmers can use to enable new
language features which are not compatible with the current
interpreter. (Glossary)

and

__future__ is a *real module*, and serves three purposes: ...
(__future__ documentation)

I suggest not to use pseudo/real module terminology and have two
definitions for __future__ in glossary: one as a name of a module and
the other as a keyword in the future statement.