Bump version to 2.2.3
Backport some test support and utilities
Unit tests around command behavior across connections

Relates to #395

(cherry picked from commit 5a380245348edd0bb9d787a623bab427b3224969)

Conflicts:
	Npgsql/NpgsqlCommand.cs
Command unsubscribe from Connection state event

Fixes #395

(cherry picked from commit 775ed000f2d900925a01420d85a6f2c93b61c3a2)

Conflicts:
	Npgsql/NpgsqlCommand.cs