git.gnome.org DOAP update

[Owen Taylor <otaylor redhat com>]

Spent some time doing some more work on handling DOAP files in the
git.gnome.org hooks. Quick summary:

 - <module>.doap is validated on commit. 

   (Validated means that my RDF/XML reading code reads it and it has
   content that looks like what we want; that does not imply it's
   actually valid RDF/XML.)

   If <modulename>.doap exists, the MAINTAINERS check is bypassed

   Note that <modulename>.doap is only validated in detail if it
   is changed. Otherwise, the check is only that it exists.

 - DOAP information for all (*) modules is collected in:
  
     http://git.gnome.org/repositories.doap 

   For modules with MAINTAINERS but no <modulename>.doap, the 
   maintainer information is extracted from MAINTAINERS and
   converted into DOAP form.

   The Git repository location is represented with the 
   gnome:GitRepository property, since there is no stand DOAP 
   property for this.

The target of the omnibus repositories.doap is other parts of our
infrastructure; for example, the script that updates module information
in LDAP could make use of this, rather than having to scrounge around
in all the git repositories itself.

In typical fashion I've left a dangling reference in the error
messages. When it fails, it says to see:

 http://live.gnome.org/MaintainersCorner#maintainers

But that still is talking about the old MAINTAINERS files and not the
new DOAP files.

- Owen

(*) All actually means "modules with maintainers information".
    Someone could fix that pretty easily, but then again, all
    modules are supposed to have maintainers information and
    in fact a DOAP file.