Packages for OCaml 4.13.0~alpha2

[Octachron]

The second alpha release for OCaml 4.13.0, with the safepoint feature integrated.

There is also few more bug fixes compared to the first alpha, and one removed feature (the removal of interbranch type propagation in pattern matching)

New feature

• 10039: Safepoints
  Add poll points to native generated code. These are effectively
  zero-sized allocations and fix some signal and remembered set
  issues. Also multicore prerequisite.
  (Sadiq Jaffer, Stephen Dolan, Damien Doligez, Xavier Leroy,
  Anmol Sahoo, Mark Shinwell, review by Damien Doligez, Xavier Leroy,
  and Mark Shinwell)

New bug fixes

• 9525, 10402: ocamldoc only create paragraphq at the toplevel of
  documentation comments
  (Florian Angeletti, report by Hendrik Tews, review by Gabriel Scherer)

• 10206: Split labels and polymorphic variants tutorials
  Splits the labels and polymorphic variants tutorial into two. Moves the GADTs
  tutorial from the Language Extensions chapter to the tutorials.
  (John Whitington, review by Florian Angeletti and Xavier Leroy)

• 10449: Fix major GC work accounting (the GC was running too fast).
  (Damien Doligez, report by Stephen Dolan, review by Nicolás Ojeda Bär and
  Sadiq Jaffer)

• 10454: Check row_more in nondep_type_rec.
  (Leo White, review by Thomas Refis)

• 10468: Correctly pretty print local type substitution, e.g. type t := ...,
  with -dsource
  (Matt Else, review by Florian Angeletti)

• 10461, 10498: caml_send* helper functions take derived pointers
  as arguments. Those must be declared with type Addr instead of Val.
  Moreover, poll point insertion must be disabled for caml_send*,
  otherwise the derived pointer is live across a poll point.
  (Vincent Laviron and Xavier Leroy, review by Xavier Leroy and Sadiq Jaffer)

• 10478: Fix segfault under Windows due to a mistaken initialization of thread
  ID when a thread starts.
  (David Allsopp, Nicolás Ojeda Bär, review by Xavier Leroy)

Removed feature

• [breaking change] 9811: remove propagation from previous branches
  Type information inferred from previous branches was propagated in
  non-principal mode. Revert this for better compatibility with
  -principal mode.
  For the time being, infringing code should result in a principality warning.
  (Jacques Garrigue, review by Thomas Refis and Gabriel Scherer)

[kit-ty-kate]

Thanks a lot!