force flagged variants to be displayed

Hi,

The QC-failed variants are behaving oddly on staging, it looks as if the db->include_failed_variations flag is being lost sometimes triggering the 'Could not find variation rs..' message when additional panels are launched from the side bar. An example is:

http://staging.ensembl.org/Homo_sapiens/Variation/Explore?v=rs16990303

If no one is looking at this one already, this PR would fix the problem.

Sarah