Changed code slightly to avoid compiler error in gcc 3.3

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403699

dlib/matrix/matrix_utilities.h

@@ -14,6 +14,7 @@
 #include <algorithm>
 #include "../std_allocator.h"
 #include "matrix_expressions.h"
+#include "matrix_math_functions.h"
 
 
 namespace dlib
@@ -1529,6 +1530,7 @@ namespace dlib
     )
     {
         using std::pow;
+        using dlib::pow;
         const typename matrix_exp<EXP>::type avg = mean(m);
 
         typedef typename matrix_exp<EXP>::type type;