Bump min vala version to 0.11.1

["Zeeshan Ali (Khattak)" <zeenix gmail com>]

Hi everyone,
   I would like to bump minimum vala version to 0.11.1 to be able to
remove some workarounds in Rygel. Another reason is that currently
rygel doesn't build against 0.11.1 and I'm not sure if it'll build
with 0.10.x anymore after I've ported it for 0.11.1. Jürg tells me
that Tracker will soon need to require it as well.

-- 
Regards,

Zeeshan Ali (Khattak)
FSF member#5124