Fix #1106 Adds support for bit fields in the MySQL PDO adapter

Hopefully this PR fixes #1106 and aid #906.
#1106 turned into a blocking issue for our project that's is already in production, that's why I'm trying to patch this one ASAP.

This is my first contribution attempt, so I'll probably need some help from you guys...
Tests seems green from here but still some details that I'm not 100% sure if they're OK, so I left some comments in the diff about this.

Also, I suppose that isn't possible to patch two or more branches in the same PR, right? I'll create a PR for `1.3.3` soon.