[MonoDevelop] Coordinate system refactoring

[Mike Krüger]

Hi
> I thought we were disallowing GTK refs in MonoDevelop.Core...
>
>    
I thought there is no reason for that anymore. Our last discussions 
about that were only structural to split the project system from the rest.
> My suggestion would be to make DomLocation 0-based and to add an
> implicit cast both ways between DocumentLocation and DomLocation.
>
>    
That would still require that they reference each other.
If we still do not need GTK refs in monodevelop core we could move the 
dom to the monodevelop.ide assembly.
Originally I implemented it here but lluis did want them into the core 
assembly ... but I don't see any structural reason for this (as well as 
the not referencing gtk# in monodevelop.core - the documentlocation 
doesn't pop up any message boxes).

Regards
Mike