Add equality between Stdlib.result and BatInnerPervasives.result

[clembu]

See #938

I agreed with the point raised by the issue author. I don't think more changes are needed. If I missed some places to put tests, I'd like to know.

[rixed]

I we do this, then batteries will become incompatible with earlier versions of the compiler.
The right way to work around this is to create the type for compiler which version is lesser than the one where the result type appeared in the Stdlib, and to equate the types after that point.
That is why we have a source preprocessor in batteries (the *.mlv and *.mliv files).

So in this case, the change should be prepended with ##V>=X## and the alternative with ##V<X##.

[rixed]

According to OCaml "Changes" file, the result type appeared in OCaml v4.08.

[clembu]

okay, I see. Makes sense. Thanks, I'll do that.

[UnixJunkie]

A possible test is to opam switch to 4.07 and compile batteries, then switch to 4.08 and recompile.
I am not sure if it is possible to unit-test this.

[hcarty]

The result type appeared in 4.03. A Result module was added in 4.08.

[clembu]

so, no need to change the type definition?
Though I may have to remove the compatibility with Legacy.Result, right? because before 4.07 that module doesn't exist?

[UnixJunkie]

For things which are version-dependant, you can use preprocessor directives, as stated before by rixed.

[clembu]

As a matter of fact, the compatibility with the Stdlib.Result module fails because Stdlib.Seq.t is not BatSeq.t. I'll look into that too.

[rixed]

Superseeded by #957