The ‘river’ module depends on generated protocol sources. These are
normally provided, indirectly, by the Wayland bar backend. But when
building plugins as shared modules, the plugins no longer depend on
the bar, and thus ‘river’ fails to build.
Fix this by doing two things:
* **Remove** the ‘river’ protocol from the ‘generic’ Wayland protocols
* Explicitly add both the generic and the ‘river’ specific protocols
to the ‘river’ module.
When downloading a copy of the f00bar repository (for example, a
released version), submodules are not included.
Thus, to enable building from such source trees, use a local copy
instead.
Note: we still keep the submodule, for easy updating.
