anchor.diff:  command instead of the package-supplied one. It can be installed following
   instructions https://gitlab.ocamlpro.com/louis/opam-custom-install[here].
   
  -In our case, we need to build the compiler (to some extent, more details later),
  -then we run `opam custom-install . -- make install`.
  +In our case, we need to build the compiler, and when we've built everything
  +that we need then we run `opam custom-install ocaml-variants -- make install`.
   This will make `opam` remove the previously installed version of the compiler
   (if any), then install the new one in its stead.
  +
  +-----
  +# reinstall the compiler, and rebuild all opam packages
  +opam custom-install ocaml-variants -- make install
  +-----
   
   Since most `opam` packages depend on the compiler, this will trigger a
   reinstallation of all the packages in the switch.
  
positive.code: 
  You can achieve some improvements using built-in `opam` commands.
  
  Using `opam install . --inplace-build --assume-built` will simply remove the
  package for the compiler, then run the installation instructions
  (`make install`) in the working directory, tracking the installed files
  correctly. The main difference with the `opam-custom-install` version
  is that there's no way to prevent this command from trigerring a full
  recompilation of your switch.
  
  You can also run `make install` manually, which will not trigger a
  
negative.code: There are no checks that it's safe to do so, so if your patch ends up
  changing even slightly one of the core libraries' files, you will likely
  get inconsistent assumptions errors later.
  
  -----
  # reinstall the compiler, leaving the opam packages untouched -- unsafe!
  opam custom-install --no-recompilations ocaml-variants -- make install
  -----
  
  Note aout the first installation:
  When you start from an empty switch, and install a compiler (in our case,
  tha `ocaml-variants` package provided by the compiler's `opam` file), then
  a number of additional packages are installed to ensure that the switch
  will work correctly. Mainly, the `ocaml` package needs to be installed,
  and while it's done automatically when using regular `opam` commands, the
  `custom-install` plugin will not force installation of dependencies.
  Moreover, if you try to fix the problem by manually installing the `ocaml`
  package, `opam` will try to recompile `ocaml-variants`, using the default
  instructions. You can get around this by running
  `opam reinstall --forget-pending` just after the `opam custom-install` command
  and just before the `opam install ocaml command`.
  Full example:
  
  -----
  opam switch create . --empty
  ./configure --prefix=$(opam var prefix) --disable-ocamldoc --disable-ocamltest
  make world && make opt
  opam custom-install ocaml-variants -- make install
  opam reinstall --forget-pending --yes
  opam install ocaml
  # You now have a working switch, in which you can start installing packages
  -----
  
  One advantage of this plugin over a plain `make install` is that it
  correctly tracks the files associated with the compiler, so if your
  