Add cancel backup capability.

This will stop the iteration of the partition objects, kill the
current twrpTar thread and remove the backup directory.

Implement TWAtomicInt class to give us a wrapper that automatically
uses mutexes before the read and write to help ensure that the
reads and writes will be atomic based on documentation.

Change-Id: I645b22bc980a292e9c7202acb24ffd22ebe68c63
diff --git a/tw_atomic.hpp b/tw_atomic.hpp
new file mode 100644
index 0000000..0f29f02
--- /dev/null
+++ b/tw_atomic.hpp
@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2015 The Team Win Recovery Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _TWATOMIC_HPP_HEADER
+#define _TWATOMIC_HPP_HEADER
+
+#include <pthread.h>
+
+class TWAtomicInt
+{
+public:
+	TWAtomicInt(int initial_value = 0);
+	~TWAtomicInt();
+	void set_value(int new_value);
+	int get_value();
+
+private:
+	int value;
+	bool use_mutex;
+	pthread_mutex_t mutex_lock;
+};
+
+#endif //_TWATOMIC_HPP_HEADER