Switch panics for not implemented store RPCS to return errors.

Previously got an "response header" ipc related issue. This will make it clearer what is going on.

Change-Id: I1a4e8f4027146c5c3fcb12a2e7e97db375876721
diff --git a/services/store/memstore/object.go b/services/store/memstore/object.go
index a0ac078..f130c7d 100644
--- a/services/store/memstore/object.go
+++ b/services/store/memstore/object.go
@@ -7,6 +7,7 @@
 	"veyron2/query"
 	"veyron2/security"
 	"veyron2/storage"
+	"veyron2/verror"
 )
 
 // object is a binding to a store value.  This is currently represented as a
@@ -88,12 +89,12 @@
 // replication groups.  Attributes are associated with the value, not the
 // path.
 func (o *object) SetAttr(pid security.PublicID, tr service.Transaction, attrs ...storage.Attr) error {
-	panic("not implemented")
+	return verror.Internalf("SetAttr not yet implemented")
 }
 
 // Stat returns entry info.
 func (o *object) Stat(pid security.PublicID, tr service.Transaction) (*storage.Stat, error) {
-	panic("not implemented")
+	return nil, verror.Internalf("Stat not yet implemented")
 }
 
 // Query returns entries matching the given query.
diff --git a/services/store/server/object.go b/services/store/server/object.go
index 96c099f..4063809 100644
--- a/services/store/server/object.go
+++ b/services/store/server/object.go
@@ -12,6 +12,7 @@
 	"veyron2/services/watch"
 	"veyron2/storage"
 	"veyron2/vdl"
+	"veyron2/verror"
 )
 
 type object struct {
@@ -216,5 +217,5 @@
 
 // Watch returns a stream of changes.
 func (o *object) Watch(ctx ipc.ServerContext, req watch.Request, stream watch.WatcherServiceWatchStream) error {
-	panic("not implemented")
+	return verror.Internalf("Watch not yet implemented")
 }
diff --git a/services/store/server/server.go b/services/store/server/server.go
index 9cad680..0404187 100644
--- a/services/store/server/server.go
+++ b/services/store/server/server.go
@@ -18,6 +18,7 @@
 	"veyron2/services/store"
 	"veyron2/services/watch"
 	"veyron2/vdl"
+	"veyron2/verror"
 )
 
 const (
@@ -263,7 +264,7 @@
 // ReadConflicts returns the stream of conflicts to store values.  A
 // conflict occurs when there is a concurrent modification to a value.
 func (s *Server) ReadConflicts(_ ipc.ServerContext, stream store.StoreServiceReadConflictsStream) error {
-	panic("not implemented")
+	return verror.Internalf("ReadConflicts not yet implemented")
 }
 
 type storeDispatcher struct {