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
Does it? That issue was reported for jQuery 2; besides, this changes
nothing in browsers other than IE<8.

-- 
Michał Gołębiowski