[Vala] Warn when invalid attributes are encountered

[Sam Thursfield <ssssam gmail com>]

Hi Vala people!
Currently I can write code in my vapi files like [CCode
(pasty_is_ripe="dogs")] and not get any warnings.

I am currently trying to write some vapi and having real trouble
getting parameters correct, various combinations of the array_*
attributes are not working at all. I figured a good first step in
debugging this would be if Vala gave some indication that it's ignored
an attribute, rather than just silently making me angry.

Are there any benefits to allowing invalid attributes or is this just
something noone has got around to implementing yet?

Thanks for your advice!!
Sam