index: write out all fields to disc

There is still now way to access what the flags mean, and the times
need to be in pure timestamp form, rather than erlang's.

Non-essential fields are allowed to be 'undefined' and then the
entry's field will remain zeroed.

test/repo_test.erl

@@ -36,7 +36,9 @@ index_add_test(Repo) ->
     {ok, Odb} = geef_repo:odb(Repo),
     {ok, BlobId} = geef_odb:write(Odb, Data, blob),
     {ok, Idx} = geef_index:new(),
-    Entry = #geef_index_entry{mode=8#100644, id=BlobId, path="README", size=size(Data)},
+    {NowMega, NowSecs, _} = os:timestamp(),
+    Time = NowMega * 1000000 + NowSecs,
+    Entry = #geef_index_entry{mode=8#100644, id=BlobId, path="README", size=size(Data), mtime=Time},
     ok = geef_index:add(Idx, Entry),
     {ok, TreeId} = geef_index:write_tree(Idx, Repo),
     Expected = geef_oid:parse("5a20bbbf65ea75ad4d9f995d179156824ccca3a1"),
@@ -44,6 +46,7 @@ index_add_test(Repo) ->
     [?_assertEqual(Expected, TreeId),
      ?_assertEqual(BlobId, Entry1#geef_index_entry.id),
      ?_assertEqual(size(Data), Entry1#geef_index_entry.size),
+     ?_assertEqual(Time, Entry1#geef_index_entry.mtime),
      ?_assertEqual(geef_index:count(Idx), 1)].
 
 ref_test(Repo) ->