Original version of scala.Enumeration to track changes

Prepares for fix of #465. Comes from commit
2fe767806b44aea3f6f53735301b11fd2ffae08b of scala/scala.
Fix #465: Adapt scala.Enumeration to not use reflection
Merge pull request #470 from gzm0/no-reflection-enum

No reflection enum
Fix #471: Adapt partest to new JSEnv structure