Add functions added in OCaml 4.10

[kit-ty-kate]

Fixes #935.

This can be viewed as a first step, some of the functions can be reproduced in batteries to avoid them being available only with OCaml 4.10

[UnixJunkie]

Hi Kate, Cc: @rixed,
No hard feelings if we ask you to resend this PR against master
once V3 is the new master?
Because, accepting this PR will force us to do yet another minor release.
While, we already anounced the latest minor release was the last.
The next release will be a major one.
Thanks,
F.

[UnixJunkie]

@kit-ty-kate no comment?
Regards,
F.

[kit-ty-kate]

I don't mind at all (sorry for not responding)

[kit-ty-kate]

Would it be ok to merge this PR now and do a release soon? The release for 4.10.0 is planned for Monday afaik (delays may apply)

[UnixJunkie]

I can merge right now.
For the "new release soon", I am not sure since it is a major release.

[UnixJunkie]

Maybe @rixed might be interested in doing the next release.

[kit-ty-kate]

For the record I can take care of submitting the release to opam-repository once a tag is available, if you prefer.

[rixed]

I have no interest in packaging, it's just toil that I do only when I need it. I'm generally happy when others do it, but I would also agree to do it regularly so this does not always fall onto the same persons.
That said, I could find time early next week to do a release.

[rixed]

Here is an error that's detected by make test when compiler is 4.10.0+rc2:

File "src/batteries_compattest.ml", line 38, characters 17-21:
38 |   module List = (List: module type of Legacy.List)
                      ^^^^
Error: Signature mismatch:
       ...
       Values do not match:
         val find_map : ('a -> 'b option) -> 'a list -> 'b
       is not included in
         val find_map : ('a -> 'b option) -> 'a list -> 'b option
       File "list.mli", line 240, characters 0-55: Expected declaration
       File "src/batList.mliv", line 461, characters 0-49: Actual declaration

[kit-ty-kate]

arf right, sorry. I have a fix.