Added missing *= operator

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403906

dlib/matrix/matrix.h

@@ -1273,6 +1273,15 @@ namespace dlib
             return *this;
         }
 
+        template <typename EXP>
+        matrix& operator *= (
+            const matrix_exp<EXP>& m
+        )
+        {
+            *this = *this * m;
+            return *this;
+        }
+
         matrix& operator += (
             const matrix& m
         )

dlib/test/matrix4.cpp

@@ -204,6 +204,16 @@ namespace
             DLIB_TEST(lr == fliplr(m));
             DLIB_TEST(ud == flipud(m));
         }
+
+        {
+            matrix<int> a, b;
+
+            a = matrix_cast<int>(round(10*randm(3,3)));
+            b = a;
+
+            b *= b;
+            DLIB_TEST(b == a*a);
+        }
     }