Allow Validator to access metadata for pending messages

Database queries for metadata only returned it for messages that were delivered already.
However, there are cases (e.g. a pending message needs to be delivered) where
the validator needs to retrieve the metadata from the database.

For these cases, a special database query has been introduced.

briar-core/src/org/briarproject/sync/ValidationManagerImpl.java

@@ -188,7 +188,7 @@ class ValidationManagerImpl implements ValidationManager, Service,
 						byte[] raw = db.getRawMessage(txn, id);
 						m = parseMessage(id, raw);
 						g = db.getGroup(txn, m.getGroupId());
-						meta = db.getMessageMetadata(txn, id);
+						meta = db.getMessageMetadataForValidator(txn, id);
 						txn.setComplete();
 					} finally {
 						db.endTransaction(txn);