Add check if different version is also included

[nlohmann]

Closes #3337

[coveralls]

Coverage remained the same at 100.0% when pulling 6be9c6f on issue3337_include_guard into ab5cecb on develop.

[falbrechtskirchinger]

Looks good to me. I hope you keep a checklist of all the places where the version number needs to be changed on release. ;-)

[nlohmann]

Looks good to me. I hope you keep a checklist of all the places where the version number needs to be changed on release. ;-)

I will need to adjust https://github.com/nlohmann/json_release_scripts for this.

[falbrechtskirchinger]

Looks good to me. I hope you keep a checklist of all the places where the version number needs to be changed on release. ;-)

I will need to adjust https://github.com/nlohmann/json_release_scripts for this.

Oh good, you have a script. Slightly off-topic: I've been using VER_TBD as a version placeholder in the documentation in one of my branches. Would you be interested in adding something more formal to your scripts? Say VER_NEXT which could be replaced in the documentation and maybe selectively in source files (e.g., JSON_HEDLEY_DEPRECATED(VER_NEXT), etc.)?

[mortenfyhn]

Fantastic!