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
This is already covered by the `support.radioValue` test. We're not duplicating `Support:` comments in other places like that; in fact, @dmethvin [removed](https://github.com/jquery/jquery/commit/d837f119c3729565103005d5d7fa89e1dd8110cb#diff-6ab16b351ac7c56aca03256aa02c3db9L67) some of them.