This uses the mysql driver library's capability to use `SET` to set the system
variables that prefixdb previously was.
Unfortunately, the library doesn't sort the params when making the string, so we
have to do a little munging to TestNewDbMap.
Ran it in a checkout of the repo since godeps now doesn't include the test files (which is great!).
```
MYSQL_TEST_ADDR=127.0.0.1:3306 go test .
ok github.com/go-sql-driver/mysql 46.099s
```
This commit updates the `go-sql-driver` dependency to the tip of master
(665b83488b90b902ce0a305ef6652e599771cdf9).
A v1.3 release and a commitment to semantic versioning[0] will soon
allow us to switch this from master to a well defined tag.
[0]
- https://github.com/go-sql-driver/mysql/issues/476#issuecomment-256004996