Fix compilation warnings and prepare to be a dependency.

src/geef_nif.erl

@@ -2,7 +2,7 @@
 %%% NIF functions, not to be used directly.
 
 -module(geef_nif).
--compile(export_all).
+-compile([export_all,nowarn_export_all]).
 
 -include("geef_records.hrl").
 
@@ -85,7 +85,7 @@ reflog_read(_Handle, _Name) ->
 reflog_delete(_Handle, _Name) ->
     ?NIF_FN.
 
-odb_object_exists(_Val, _Val) ->
+odb_object_exists(_Val1, _Val2) ->
     nif_error(?LINE).
 
 -spec odb_write(term(), iolist(), atom()) -> term().