BUG: Fix bug when pulling in href'd xincludes.

Additional xmf files are now read in via href'd xincludes which broke
mapping of xmlNodePtrs to XdmfItems (which qas necessary to enable shared
pointer representation in file).  This mapping was fixed.

core/XdmfCoreReader.cpp

@@ -58,7 +58,12 @@ public:
   {
     mXPathMap.clear();
     xmlXPathFreeContext(mXPathContext);
-    xmlFreeDoc(mDocument);
+    for(std::map<std::string, xmlDocPtr>::const_iterator iter = 
+	  mDocuments.begin(); iter != mDocuments.end(); ++iter) {
+      xmlFreeDoc(iter->second);
+    }
+    mDocuments.clear();
+    
     xmlCleanupParser();
   }
 
@@ -79,6 +84,8 @@ public:
                          " in XdmfCoreReader::XdmfCoreReaderImpl::openFile");
     }
 
+    mDocuments.insert(std::make_pair((char*)mDocument->URL, mDocument));
+
     mXPathContext = xmlXPtrNewContext(mDocument, NULL, NULL);
     mXPathMap.clear();
   }
@@ -127,11 +134,20 @@ public:
             currAttribute = currAttribute->next;
           }
 
-          xmlDocPtr document = NULL;
           xmlXPathContextPtr context = mXPathContext;
           if(href) {
+	    xmlDocPtr document;
             xmlChar * filePath = xmlBuildURI(href, mDocument->URL);
-            document = xmlReadFile((char*)filePath, NULL, 0);
+	    std::map<std::string, xmlDocPtr>::const_iterator iter = 
+	      mDocuments.find((char*)filePath);
+	    if(iter == mDocuments.end()) {
+	      document = xmlReadFile((char*)filePath, NULL, 0);
+	      mDocuments.insert(std::make_pair((char*)document->URL, document));
+	    }
+	    else {
+	      document = iter->second;
+	    }
+
             context = xmlXPtrNewContext(document, NULL, NULL);           
           }
 
@@ -148,7 +164,6 @@ public:
 
           if(href) {
             xmlXPathFreeContext(context);
-            xmlFreeDoc(document);
           }
 
         }
@@ -244,6 +259,7 @@ public:
   }
 
   xmlDocPtr mDocument;
+  std::map<std::string, xmlDocPtr> mDocuments;
   const XdmfCoreReader * const mCoreReader;
   const shared_ptr<const XdmfCoreItemFactory> mItemFactory;
   const std::string mRootItemTag;