Record IO C++ binding: non-empty vector of strings does not work

It works in the binary case, but not in CSV or XML.

Here is the code to put some strings in the vector.

std::vector<std::string>& v = r1.getVectorVal();
v.push_back("hello");
v.push_back("world");

In the CSV file, the strings appear twice, for some reason. In the XML file they appear three times.