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
@dmethvin proposed to go the other way round and I agree; I don't think duplicating such comments is needed; it's not DRY. It's clear here that this one is needed for browsers that misbehave on the `input` support test; the rest is documented over the test itself.