Print warning if using deprecated java.level with new enough parent POM

[basil]

Tested manually with jenkinsci/plugin-pom#522

[jglick]

I think you could do this with a POM profile, but since we have a place in Java code to do it, may as well!

[basil]

I couldn't find a way to do this with a POM profile. Enforcer has a requireProperty rule, but here we want to do the opposite (ban a property).

[basil]

I think you could do this with a POM profile

Actually I think not. From the Maven documentation on profiles:

Supported variables are system properties like ${user.home} and environment variables like ${env.HOME}. Please note that properties and values defined in the POM itself are not available for interpolation here.

So yeah this is just not possible.