scilab-bin: Add 'scilab' executable to PATH, so as to make it integrate better into SageMath

[fusion809]

Issue description

The scilab-bin package works fairly well, but unfortunately it doesn't add a scilab executable to PATH, rather its executables in PATH are named scilab-6 and scilab-6.0.1. This has an undesirable consequence, other than requiring users to type in extra characters when launching it from the command-line, which is that SageMath, installed via the sage package, cannot seem to call it when you try to use it within SageMath Notebook.

Here is a screenshot showing you what I mean:

Steps to reproduce

Install SageMath on NixOS 18.09, with nix-env -f '<nixos-unstable>' -iA sage and Scilab with nix-env -f '<nixos-unstable>' -iA scilab-bin. Then, start SageMath with sage and start the notebook with notebook() at the sage> prompt. Then, after setting an admin password, create a new notebook, select from the dropdown menu labelled in the above screenshot "scilab (optional)". Then, in a new cell, type in whatever Scilab command you want (e.g. 3^3 will do) and click the "evaluate" button. If you get the error shown in the above screenshot, then you have observed this bug.

Technical details

$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 4.14.84, NixOS, 18.09.1446.db561c90ef3 (Jellyfish)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.1.3`
 - channels(fusion809): `""`
 - channels(root): `"nixos-18.09.1446.db561c90ef3, nixos-unstable-19.03pre159472.80738ed9dc0"`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

[fusion809]

Adding a scilab executable to PATH manually, like with symlinks, manages to fix this issue FYI.