[glom] Box_DataDetails::fill_from_database(): Correctly find the primary key.

[Murray Cumming <murrayc src gnome org>]

commit 247442e6ea7eaf6c29a78720cdd1799569e4eacd
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Jan 27 11:01:51 2016 +0100

    Box_DataDetails::fill_from_database(): Correctly find the primary key.
    
    This was a regression caused by use of auto in this commit:
    
https://git.gnome.org/browse/glom/commit/glom/mode_data/box_data_details.cc?id=37a00864fc3fa2f96b75ebb83f97a61628592df2

 glom/mode_data/box_data_details.cc |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/glom/mode_data/box_data_details.cc b/glom/mode_data/box_data_details.cc
index 8d632d1..a273b1d 100644
--- a/glom/mode_data/box_data_details.cc
+++ b/glom/mode_data/box_data_details.cc
@@ -327,8 +327,9 @@ bool Box_Data_Details::fill_from_database()
               continue;
 
             //Compare the relationship and related relationship:
-            auto uses_a = layout_item_pk;
-            auto uses_b = element;
+            //Don't use auto here. We need to compare them as UsesRelationship.
+            const std::shared_ptr<const UsesRelationship> uses_a = layout_item_pk;
+            const std::shared_ptr<const UsesRelationship> uses_b = element;
             if(*uses_a == *uses_b)
             {
               index_primary_key = i;