Suppress override on iface ToString decls.
Suppress override on iface ToString decls.

* generator/Method.cs: interface method declarations do not support or
need an override keyword, so block the generation of it when the implementor
and container_type indicate generation of the iface itself.

orion75/gtk-sharp,Gankov/gtk-sharp,akrisiun/gtk-sharp,orion75/gtk-sharp,Gankov/gtk-sharp,Gankov/gtk-sharp,akrisiun/gtk-sharp,openmedicus/gtk-sharp,orion75/gtk-sharp,openmedicus/gtk-sharp,sillsdev/gtk-sharp,Gankov/gtk-sharp,Gankov/gtk-sharp,akrisiun/gtk-sharp,akrisiun/gtk-sharp,antoniusriha/gtk-sharp,openmedicus/gtk-sharp,sillsdev/gtk-sharp,antoniusriha/gtk-sharp,orion75/gtk-sharp,openmedicus/gtk-sharp,openmedicus/gtk-sharp,openmedicus/gtk-sharp,antoniusriha/gtk-sharp,sillsdev/gtk-sharp,Gankov/gtk-sharp,antoniusriha/gtk-sharp,orion75/gtk-sharp,sillsdev/gtk-sharp,sillsdev/gtk-sharp,akrisiun/gtk-sharp,antoniusriha/gtk-sharp,openmedicus/gtk-sharp