To build lang/processing, one needs a specific version of the JDK (as
specified in
https://github.com/processing/processing/blob/master/build/build.xml).
Question: how does one create a dependency in the Portfile to determine
whether this version is present? The purpose is to 1) provide a better
error message to the user and 2) prevent builds from failing
https://travis-ci.org/macports/macports-ports/builds/423195489 at every
update. I tried checking for the existence of this folder: `/Library/Java/
JavaVirtualMachines/jdk1.8.0_181.jdk/` but didn't get anywhere. Thanks!
