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
Don't we still need to use `jQuery.valHooks.option.get( option )` instead of `option.value`? It's still [defined](https://github.com/mzgol/jquery/blob/drop-old/src/attributes/val.js#L74).