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
For reference, it was added in https://github.com/jquery/jquery/commit/877306738f931a711c41d907e69fc8930f985830