a bit more robust error messaging when deleting files in a torrent

include/libtorrent/torrent.hpp

@@ -280,7 +280,7 @@ namespace libtorrent
 
 		bool should_check_files() const;
 
-		void delete_files();
+		bool delete_files();
 
 		// ============ start deprecation =============
 		void filter_piece(int index, bool filter);

src/session_impl.cpp

@@ -5279,7 +5279,13 @@ retry:
 
 		torrent& t = *i->second;
 		if (options & session::delete_files)
-			t.delete_files();
+		{
+			if (!t.delete_files())
+			{
+				if (alerts().should_post<torrent_delete_failed_alert>())
+					alerts().post_alert(torrent_delete_failed_alert(t.get_handle(), error_code()));
+			}
+		}
 
 		tptr->update_guage();
 

src/torrent.cpp

@@ -6976,7 +6976,7 @@ namespace libtorrent
 		return limit;
 	}
 
-	void torrent::delete_files()
+	bool torrent::delete_files()
 	{
 		TORRENT_ASSERT(m_ses.is_network_thread());
 
@@ -6992,7 +6992,9 @@ namespace libtorrent
 			TORRENT_ASSERT(m_storage);
 			m_storage->async_delete_files(
 				boost::bind(&torrent::on_files_deleted, shared_from_this(), _1, _2));
+			return true;
 		}
+		return false;
 	}
 
 	void torrent::clear_error()