mysql-native v3.2.0 - the safe update

[Steven Schveighoffer]

It's happened. I opened the PR over 2 years ago, and just got around to 
bringing it up to date in the last few days.

This is a huge huge update. I've never done anything like this before, 
but I think it works as a drop-in replacement, while allowing you to 
migrate any piece you wish from unsafe code to safe code. Please let me 
know if there are *any* problems you find with this.

See the [safe migration 
doc](https://github.com/mysql-d/mysql-native/blob/master/SAFE_MIGRATION.md) 
for more details.

Note this does *not* build with dip1000, because the two underlying 
libraries (Phobos sockets and vibe.d) do not build as safe with dip1000.

-Steve