compile gflags correctly, remove google namespace, use gflags instead, port all code using it

examples/cpp/linear_programming.cc

@@ -119,7 +119,7 @@ void RunAllExamples() {
 }  // namespace operations_research
 
 int main(int argc, char** argv) {
-  google::ParseCommandLineFlags( &argc, &argv, true);
+  gflags::ParseCommandLineFlags( &argc, &argv, true);
   operations_research::RunAllExamples();
   return 0;
 }