trunk preprocessor: in NumericalConstants

* fixed bug introduced in r2642 with NaN
* added a check to verify that the conversion to double succeeded (use strtod() instead of atof())
* store the double values in a vector


git-svn-id: https://www.dynare.org/svn/dynare/trunk@2647 ac1d8469-bf42-47a9-8791-bf33cf982152