gapi: Plumb through a URI mechanism

This is at least a stop-gap until we redo the whole filesystem API mess.
I think golang is partly to blame because they don't have proper API's
merged yet.

yamlgraph/gapi.go

@@ -114,6 +114,13 @@ func (obj *GAPI) Init(data *gapi.Data) error {
 	return nil
 }
 
+// Info returns some data about the GAPI implementation.
+func (obj *GAPI) Info() *gapi.InfoResult {
+	return &gapi.InfoResult{
+		URI: obj.InputURI,
+	}
+}
+
 // Graph returns a current Graph.
 func (obj *GAPI) Graph() (*pgraph.Graph, error) {
 	if !obj.initialized {