potential locale issues with readScalar

We currently have two forms of readScalar. One that uses Istream/token and the second that uses strtof or strtod internally. Both strtof and strtod are apparently locale-dependent (cf, http://www.cplusplus.com/reference/cstdlib/strtod/).

Although it doesn't help with locale, but could also consider using the newer std::stof or std::stod instead, since these work with std::string directly. In any case, it would be nice to reduce the number of places with this type of code:

readScalar(IStringStream(str)());

We could quite reasonable either bury the IStringStream inside, or equivalent, so that we could simply use

readScalar(str);