Entity field access condition 2281113b

Updated version of my previous patch;  I've changed branches due to some very bad problems with "git rebase".

I'm aware I have two commits that appear here.  That's the problem -- I can't get git to go lower without pulling in commits I don't own.  If you folks can tell me how to fix this, much thanks.

The patch creates the plugin and test for the issue.
> Really not required though. We can work through this together if you like (using simpletest) or you can give Unit tests a shot (which I am going to help you with too then). The existing unit tests should give you a good idea of what's going on.
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I actually know PHPUnit a lot better than SimpleTest (I'm using a back-ported version of the D8 system in a couple of D7 projects), so I'm fine with that. 

Just show me where the PHPUnit tests go, and what test class you want me to derive from.

Thanks,
Rob