new getUnits method in ControlGraphics

[Angus Leeming]

As "data" is a static variable, shouldn't this function return a 
reference?

Angus

vector<string> const ControlGraphics::getUnits()
{
        static vector<string> data;
        if (!data.empty())
                return data;

        data.resize(bb_size);
        for (lyx::size_type i = 0; i < bb_size; ++i) {
                data[i] = bb_units[i];
        }
        return data;
}