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
The specific problem with `defaultValue` doesn't seem to be present in IE9, I just did a quick check and it survives a cloning now. So it seems like that code is unnecessary in master.