Don't waitpid on SIGCHLD, which lost the retcode (#11)

* Don't waitpid on SIGCHLD, which lost the retcode

* Adding test

subprocess.hpp

@@ -1150,11 +1150,6 @@ inline void Popen::execute_process() throw (CalledProcessError, OSError)
   }
   exe_name_ = vargs_[0];
 
-  std::signal(SIGCHLD, [](int sig){
-    int status;
-    waitpid(-1, &status, WNOHANG);
-  });
-
   child_pid_ = fork();
 
   if (child_pid_ < 0) {

test/test_ret_code.cc

@@ -0,0 +1,18 @@
+#include <iostream>
+#include "../subprocess.hpp"
+
+namespace sp = subprocess;
+
+void test_ret_code()
+{
+  std::cout << "Test::test_poll_ret_code" << std::endl;
+  auto p = sp::Popen({"/bin/false"});
+  while (p.poll() == -1) {
+    usleep(1000 * 100);
+  }
+  assert (p.retcode() == 1);
+}
+
+int main() {
+  test_ret_code();
+}