Release references to out-of-scope JUnit framework objects

In this release, references to JUnit framework objects are released when these objects pass out-of-scope. This should resolve excessive memory utilization problems associated with large test suites.

Previously, references were retained for the lifetime of the Java instance that hosted test execution. If the test collection was relatively modest, this didn't constitute a significant issue. However, the accumulation of objects during the execution of large suites of tests could result in out-of-memory failures.