Mode 1748 - Fixed the VersionExceptions thrown when importing XML content into system view

The problem is identical to the one reported for 2.x, via https://issues.jboss.org/browse/MODE-1450.

The fix however, was a bit more complicated because in 3.x the JCR layer has changed. The fix involved adding a new boolean flag _skipVersioningValidation_ to the protected methods _addChild_ and _setProperty_ in the JCR layer.

The test case reproducing this issue is based on the attached file from https://issues.jboss.org/browse/MODE-1748.