Re #6811. Forward call to AlgorithmManager's cancelAll method.

This is better than pulling out the algorithm list and manipulating
things up the top.

Code/Mantid/MantidPlot/src/Mantid/AlgorithmMonitor.cpp

@@ -141,14 +141,8 @@ void AlgorithmMonitor::cancel(Mantid::API::AlgorithmID id)
 /** Cancel all running algorithms */
 void AlgorithmMonitor::cancelAll()
 {
-  const std::deque<IAlgorithm_sptr>& algs = Mantid::API::AlgorithmManager::Instance().algorithms();
-  for(std::deque<IAlgorithm_sptr>::const_iterator a = algs.begin(); a != algs.end(); ++a)
-  {
-    if ( std::find(m_algorithms.begin(), m_algorithms.end(), (**a).getAlgorithmID()) != m_algorithms.end() )
-    {
-      (**a).cancel();
-    }
-  }
+  // Forward to the AlgorithmManager
+  AlgorithmManager::Instance().cancelAll();
 }