Added more DatabaseComponent unit tests, tightened up existing tests.

briar-api/src/net/sf/briar/api/db/DatabaseComponent.java

@@ -259,6 +259,12 @@ public interface DatabaseComponent {
 	/** Removes a contact (and all associated state) from the database. */
 	void removeContact(ContactId c) throws DbException;
 
+	/**
+	 * Removes a transport (and any associated configuration and local
+	 * properties) from the database.
+	 */
+	void removeTransport(TransportId t) throws DbException;
+
 	/**
 	 * Sets the connection reordering window for the given endoint in the given
 	 * rotation period.