remove lot of duplicated code. The design of the format is not ideal but

remove lot of duplicated code. The design of the format is not ideal but
is a bit late to change. So I prefer to iterate once per inheritance
level to find corresponding tags, slower, but not really noticiable.
Also remove warnings about unknowwn tags found because
3 different functions now parse the same dom looking
for different tags. The validation is done via relaxng anyway.

So now, only 1 function parsing dependencies, and 1 looking for
resolvable common data.