Melting pot with `-c ... -p` flags fails

[ctrueden]

I probably broke the melting pot's support for pruning out components not depending on a changed component. In pom-scjiava I ran:

tests/run.sh -c net.imagej:imagej-common:2.0.0-SNAPSHOT -p

Hoping I could build a mega-melt that tested only components depending on imagej-common, against a locally-built imagej-common 2.0.0-SNAPSHOT I had installed. But during the pruning phase, it died with:

[INFO] Checking relevance of component net.imagej/imagej-legacy
[INFO] Checking relevance of component net.imagej/imagej-matlab
[INFO] Checking relevance of component net.imagej/imagej-mesh-io
[ERROR] CannotMelting pot generation failed!

Would be nice to make this scenario work.