Misc: Drop support for older browsers; update support comments

That includes IE<8, Opera 12.x, Firefox<29, Safari<6.0 and some hacks
for old Blackberry.

Fixes gh-1836
Fixes gh-1701
Refs gh-1815
Refs gh-1820
To clarify that policy: In cases where there is a `support.x` value being used I don't think we need the comment, but we do in other places where we do stuff a non-obvious way to avoid some browser bug.