add bool return value so diagnostics are easier

Source/cmSystemTools.cxx

@@ -749,13 +749,15 @@ void cmSystemTools::Message(const char* m1, const char *title)
 }
 
 
-void cmSystemTools::CopyFileIfDifferent(const char* source,
+bool cmSystemTools::CopyFileIfDifferent(const char* source,
                                         const char* destination)
 {
   if(cmSystemTools::FilesDiffer(source, destination))
     {
     cmSystemTools::cmCopyFile(source, destination);
+    return true;
     }
+  return false;
 }
 
   

Source/cmSystemTools.h

@@ -174,7 +174,7 @@ public:
    * Copy the source file to the destination file only
    * if the two files differ.  
    */
-  static void CopyFileIfDifferent(const char* source,
+  static bool CopyFileIfDifferent(const char* source,
                                   const char* destination);
   
   ///! Compare the contents of two files.  Return true if different.