exports: Add cmExportSetMap class

This is a map<string, cmExportSet *> with overloaded operator[] and destructor.

Source/cmExportSetMap.cxx

@@ -0,0 +1,34 @@
+/*============================================================================
+  CMake - Cross Platform Makefile Generator
+  Copyright 2000-2012 Kitware, Inc., Insight Software Consortium
+
+  Distributed under the OSI-approved BSD License (the "License");
+  see accompanying file Copyright.txt for details.
+
+  This software is distributed WITHOUT ANY WARRANTY; without even the
+  implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+  See the License for more information.
+============================================================================*/
+
+#include "cmExportSetMap.h"
+#include "cmExportSet.h"
+
+cmExportSet* cmExportSetMap::operator[](const std::string &name)
+{
+  std::map<std::string, cmExportSet*>::iterator it = this->find(name);
+  if (it == this->end()) // Export set not found
+    {
+    it = this->insert(std::make_pair(name, new cmExportSet(name))).first;
+    }
+  return it->second;
+}
+
+cmExportSetMap::~cmExportSetMap()
+{
+  for(std::map<std::string, cmExportSet*>::iterator it = this->begin();
+      it != this->end();
+      ++ it)
+    {
+    delete it->second;
+    }
+}