Accidentally removed a needed #include yesterday. Just putting it back.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%404084

dlib/xml_parser.h

@@ -12,6 +12,7 @@
 #include "map.h"
 #include "stack.h"
 #include "sequence.h"
+#include "memory_manager.h"
 
 
 namespace dlib