Add fields for replication support.

src/osmformat.proto

@@ -62,6 +62,19 @@ message HeaderBlock {
 
   optional string writingprogram = 16; 
   optional string source = 17; // From the bbox field.
+
+  /* Tags that allow continuing an Osmosis replication */
+
+  // replication timestamp, expressed in seconds since the epoch, 
+  // otherwise the same value as in the "timestamp=..." field
+  // in the state.txt file used by Osmosis
+  optional int64 osmosis_replication_timestamp = 32;
+
+  // replication sequence number (sequenceNumber in state.txt)
+  optional int64 osmosis_replication_sequence_number = 33;
+
+  // replication base URL (from Osmosis' configuration.txt file)
+  optional string osmosis_replication_base_url = 34;
 }