Added some missing #includes needed when compiling with visual studio 7.1

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403333

dlib/test/discriminant_pca.cpp

@@ -7,6 +7,7 @@
 #include <dlib/string.h>
 #include <vector>
 #include <sstream>
+#include <ctime>
 
 namespace  
 {

dlib/test/empirical_kernel_map.cpp

@@ -7,6 +7,7 @@
 #include <dlib/string.h>
 #include <vector>
 #include <sstream>
+#include <ctime>
 
 namespace  
 {