libnautilus-extension: remove the ability to add toolbar items

[Pierre Wieser <pwieser trychlos org>]

Hi,

The NautilusMenuProvider::get_toolbars_items() interface method
has been removed from the master.

This interface was here since literally years, and I may safely
suppose that several extensions used it, and are so broken down
now (e.g. tracker which now blocks when trying to jhbuild it).

I so have two questions for the list.

Is it possible to have some sort of rationale ? I am curious about
it (and, yes, I have read the commit comment which is a bit short
for my curiosity)

Does Nautilus have some sort of runtime version that we could check
at runtime, so that an extension would be able to dynamically address 
the interface if it exists ?
Or do we have to compile our extensions against specific versions
of Nautilus ?

Regards
Pierre