Make iPhone 6+ behave more sensibly.

The iPhone 6+ behaves badly without this.  It returns a density of 1 which makes apps think its a very very large screen (vs a regular screen with very small pixels). Note that this also affects ppiX & ppiY (et al), but in an appropriate way.

This is not a perfect fix for density on iOS, but it's a decent bandaid for now.
Merge pull request #2488 from eggheadgames/master

Make iPhone 6+ behave more sensibly.