(#2781) - rollback to websql on safari/ios 8

Yeah, I know: I'm finally resorting to browser-sniffing. Even though we have [a working reproducible test](http://bl.ocks.org/nolanlawson/c83e9039edf2278047e9).

But listen, I have a life outside of this open-source project, or at least I'm desperately trying to have one. And I just do not have time to rearchitect our entire adapter validation logic to make it asynchronous so we can detect a dumb bug that hopefully the WebKit devs will fix soon anyway. At the very least, I can spend my time fixing more important issues in PouchDB (like our skimpy documentation).

Submitting this as-is. Saucelabs doesn't support Safari 7.1 or iOS 8 yet, so you'll have to take my word for it that it passes.

I look forward to when we can revert this commit.