Expose transactions through DatabaseComponent interface.

briar-api/src/org/briarproject/api/db/Transaction.java

@@ -0,0 +1,15 @@
+package org.briarproject.api.db;
+
+/** A wrapper around a database transaction. */
+public class Transaction {
+
+	private final Object txn;
+
+	public Transaction(Object txn) {
+		this.txn = txn;
+	}
+
+	public Object unbox() {
+		return txn;
+	}
+}