mysql-native v2.2.1: Bugfixes

[Nick Sabalausky (Abscissa)]

An all-D MySQL/MariaDB client library:
https://github.com/mysql-d/mysql-native
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Tagged bugfix release, 'v2.2.1'.

Full changelog:
https://github.com/mysql-d/mysql-native/blob/master/CHANGELOG.md

This fixes a pretty big regression (for vibe.d users) from v2.1.0 (#170: 
Assertion when concurrently using multiple LockedConnection), as well as 
a few other issues for users of the latest DMD (2.079.0) and vibe.d (0.8.3).