Added a pragma to disable a warning from visual studio 2012.

dlib/vectorstream/vectorstream.h

@@ -12,6 +12,14 @@
 #include <cstdio>
 #include "../algs.h"
 
+
+#ifdef _MSC_VER
+// Disable the warning about inheriting from std::iostream 'via dominance' since this warning is a warning about
+// visual studio conforming to the standard and is ignorable.  See http://connect.microsoft.com/VisualStudio/feedback/details/733720/inheriting-from-std-fstream-produces-c4250-warning
+// for further details if interested.
+#pragma warning(disable : 4250)
+#endif // _MSC_VER
+
 namespace dlib
 {
     class vectorstream : public std::iostream