prov/commit

FIXED: can no longer rely on access_file to silently fail on http uris

diff --git a/lib/prov_schema.pl b/lib/prov_schema.pl
index 55b23d6..c5692d5 100644
--- a/lib/prov_schema.pl
+++ b/lib/prov_schema.pl
@@ -206,8 +206,14 @@ log_entity_create(File, Options) :-
     option(prov(ProvBundle), Options),
     option(graph(Graph), Options, none),
     (   uri_is_global(File)
-    ->  Entity = File
-    ;   uri_file_name(Entity, File)
+    ->  Entity = File,
+        xsd_now(TimeStamp)
+    ;   uri_file_name(Entity, File),
+        (   access_file(File, read),
+            time_file(File, Time)
+        ->  xsd_timestamp(Time, TimeStamp)
+	;   xsd_now(TimeStamp)
+        )
     ),
     xsd_now(TimeStamp),
     rdf_assert(Entity, rdf:type, prov:'Entity', ProvBundle),