The class FGAerodynamics currently catches std::string exceptions thrown by the constructor of FGFunction. However FGFunction is now throwing a mix of exceptions deriving from both std::string and JSBSim::BaseException, so FGAerodynamics is no longer catching all exceptions thrown by the constructor of FGFunction.

This PR is changing:

• the remaining std::string exceptions in FGFunction to JSBSim::BaseException
• the format of exceptions caught by FGAerodynamics from std::string to JSBSim::BaseException.

Also the try/catch block in FGAerodynamics is simplified in the process. Currently the code looks like:

if (condition) {
  try {
    function1 = new FGFunction();
  }
  catch (const string& str) {
    log << "Fatal error: " << str;
  }
}
else {
  try {
    function2 = new FGFunction();
  }
  catch (const string& str) {
    log << "Fatal error: " << str;
  }
}

This PR avoids the duplication of the try/catch block by moving the if/else condition into the try block:

try {
  if (condition) {
    function1 = new FGFunction();
  } else {
    function2 = new FGFunction();
  }
}
catch (const BaseException& e) {
    log << "Fatal error: " << e.what();
}