Improvements for filter implicit join to address the bug identified as JENA-692
The transformation is now more careful about checking whether it is valid to apply over union
It is also now capable of special casing unions where one branch can be seen to always evaluate to false in advance

Add various tests cases for these changes

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1594256 13f79535-47bb-0310-9956-ffa450edef68