Memory leak in stateless session when using CommandFactory.newInsertElements()

Description of problem:
There is a memory leak when calling an execute method on
StatelessKnowledgeSession with list of Commands(facts). See the reproducer.

According to heap dump, the
org.drools.command.runtime.rule.InsertElementsCommand is holding references to
facts even after the execute() method is finished.

This is a regression from 5.1.0 GA.

Version-Release number of selected component (if applicable):
BRMS 5.2.0 ER3

How reproducible:
Always

Steps to Reproduce:
1. Run the attached reproducer with ER3 binaries on classpath.
2. Look at stdout to see the raising heap used memory.

Actual results:
Heap used memory is raising.

Expected results:
Heap used memory is not raising. All unused object are collected.

Additional info:
When jBPM jars are not included in classpath, leak is away and memory usage in
not raising.

Memory leak does not occur when StatefulKnowledgeSession is used.

Reported in bugzilla as: https://bugzilla.redhat.com/show_bug.cgi?id=734367