awesome wm: Focus steal hardened rc.lua

[David Hobach]

Dear users,

I was annoyed by some unwanted focus changes whilst using awesome and
thus created the attached config that should prevent most of them. Maybe
it'll be useful to some of you (I noticed some threads on this mailing
list about focus steal stuff after all).

The code should be rather self-explanatory for anyone interested.

@Devs: Not sure whether you'd be interested to push parts of that upstream.

Kind Regards
David