manual: post GPR#305 update (allow exceptions under or-patterns)

This week we merged several changes from Thomas Refis, to allow the
use of exception patterns under or-patterns, to write code such as

  match foo x with
    | None | exception Not_found -> ...
    | Some -> ...

Unfortunately, I failed to properly assess the impact of this change,
and in particular to make sure that Luc Maranget had properly reviewed
this code -- any change to the pattern-matching machinery should be
reviewed by Luc.

The problem that I had not foreseen and that he would have immediately
realized is that, while adapting the pattern-matching *compiler* is
relatively easy (Thomas inserted a transformation at the right place
to separate exception patterns from the others and handle them
separately, using the staticraise construct used by the
pattern-matching compiler to avoid duplicating the
right-hand-side branch), adapting the pattern-matching warnings
machinery is both more subtle and easier to overlook (it may fail
silently and nobody notices, unlike wrong code production). This part
of the compiler is subtle and best understood by Luc, but he does not
have the time to do a proper review of those changes in the timeframe
for the 4.03 feature freeze (mid-December).

I believe the right move in this case, implemented in the present
commit, is to revert the change from trunk (this is not a feature that
we must *imperatively* have in 4.03), do a proper job of understanding
the changes, and integrate the change when we are confident it is
ready. I hope to do this in 2016, together with Luc Maranget and
Thomas Refis -- hopefully this would allow Thomas and I to be more
confident when changing the pattern-matching machinery in the future.

Revert "Merge pull request #343 from trefis/pr7083"
This reverts commit 22681b8, reversing
changes made to a24e4ed.

Revert "Merge pull request #341 from trefis/or-exception"
This reverts commit f8f68bd, reversing
changes made to 1534fe8.

Revert "Merge pull request #305 from trefis/or-exception"
This reverts commit cfeda89, reversing
changes made to 77cf36c.

This ensures that the site name is referenced in the toplevel bar

Closes ocaml#341

* Closes ocaml#341, show and install the latest version

This fixed ocaml#341 and teaches the user how to show the latest version of the compiler and install it.
This will also help them upgrade in the future if they desire.

Co-authored-by: Thibaut <[email protected]>