Fix bugs 9190 and 9193.

Fix bugs 9190 and 9193.

The conversion from floating point to string performed by
boost:lexical_cast does not allow specifying a precision and,
for example, values such as 0.9 are returned as 0.899999976.
The standard C++ way for performing the conversion is using
std::ostringstream which is exempt from this problem, even if
less efficient. For the sake of accuracy, boost::lexical_cast
is ditched in favor of the ostrinsgstream implementation.
In C++11 another option would be using std::to_string, but I
think it is not as efficient as the boost way and not worth
implementing through #ifdef's.