[Vala] Vapigen that validates .metadata entries + output symbol file

[Daniel Hams <daniel hams gmail com>]

Hi all,

Just a quick mail to announce to those interested I have put a patch in
bugzilla that refactors the .metadata handling in vapigen. Patch applies
to HEAD. 


Changes to vapigen:

* Check if the metadata attributes (is_array, ellipsis etc) are
applicable to the symbol they are placed on. If they are not, a warning
is generated

* Enumerate explicitly all metadata attribute keywords inside the vala
code

* Centralise parsing/split to double/int/comma delimited etc into one place

* Allow output of a symbols file containing a list of valid attribute keys
for each symbol discovered during execution

I have regression tested the changes against the existing .vapi packages in 
git and the changes pass regeneration tests there.

For reference, this patched vapigen did actually find some .metadata errors 
in the existing git package .metadata files - so it seems to be useful.

Cheers,

Dan