+ systematic handling of directories in AbstractModuleCompilationTests
  - no more ad-hoc use of 'javac' path segment
  - no longer pass 'output' parameter from individual tests
  + generally let ecj compile from 'src' to 'bin'
  + generally let javac compile from 'src' to 'javac'
+ when walking output files don't delete (for later inspection)
  + map ecj-output paths to expected javac-output paths
  - soften output when javac creates fewer classfiles in negative tests
+ support verifying classfiles from both compilers

PR https://github.com/eclipse-jdt/eclipse.jdt.core/pull/3619