Require valac >= 0.22.1

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
glib >= 2.41.2 and valac < 0.25.2 not compatible

Since glib 2.41.2, the mutex/cond implementation on Linux has changed.
The code compiled with Vala < 0.26 which targets at least glib 2.32 with
--target-glib 2.32 will suffer from deadlocks.

Your options are either:
- Do not --target-glib 2.32
- Update Vala to at least 0.25.2
- Downgrade glib

https://mail.gnome.org/archives/vala-list/2014-December/msg00018.html

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>