pert:
Yeah, they didn't really think enough about making new versions of the boards packages compatible with old versions of the IDE. Before Boards Manager that wasn't an issue but if they're going to pop up a notification in the IDE telling you to update to the new boards then they definitely need to make sure it's not going to break things when you do it. I did do a couple of things to try to fix that and I don't know of any backwards compatibilities going forward and hopefully the developers will consider that in their future work. Sometimes you just have to break backwards compatibility to move forward but that should definitely be well documented and in this case the fixes were actually really simple.
I did a little research afterwards and found your name in the first thread that I opened 
pert:
I hope you will enjoy 1.8.5. I really didn't like 1.6.6 so I'm surprised you were happy with that particular version so long.
If you don't know what you miss, you can be happy forever with what you have 
I'm not somebody that upgrades software for the sake of 'the latest and the greatest' but was considering it due to the local include issue.
Anyway, I quickly checked the local include directory sketch that I have and that now works Any idea (from memory, no need for research) in which IDE version it was fixed?