Fix for missing class loader in AbstractDiffGenerator.
Qualified exceptions added, Policy tests fixed, several bugs fixed.
Updated to core version 1.4.1.11.
Private tests removed.
Updated .gitignore for IntelliJ IDEA project files
Partial fix for #158 .

When an element is compared it now first checks if the other element has the 'type' property, avoiding a MissingPropertyException. When a choice is compared it now first check if the other entity has the 'elements' propery, avoiding a MissingPropertyException.

A Difference is created on both occasions, but without a proper message.
Merge pull request #163 from ithena/158-fix-simple-to-choice

Partial fix for issue #158 where the compare algorithm fails when an Element has changed to a Choice or vice versa