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
I agree we should always provide versions. We've had `// Support: IE` in a couple of places and it's a PITA as I never know if it's still needed etc.

> Of course this is complicated because lately Microsoft has been slipstreaming fixes into IE11, but I don't know that any of those include patches we've addressed.

It does, you even LGTM'd my PR removing one of them. ;) https://github.com/jquery/jquery/pull/1901