Gsdx: Move the stdext namespace declaration.

This will eventually lead to
error C2871: 'stdext' : a namespace with this name does not exist.
might as well fix it now.

plugins/GSdx/stdafx.h

@@ -131,9 +131,9 @@ using namespace std;
 	#else
 	#include <hash_map>
 	#include <hash_set>
+	using namespace stdext;
 	#endif
 
-	using namespace stdext;
 
 	// hashing algoritms at: http://www.cris.com/~Ttwang/tech/inthash.htm
 	// default hash_compare does ldiv and other crazy stuff to reduce speed