Remove NR_INF and replace by std::numeric_limits implementation
Kill nr_nan and precinit

use std::numeric_mits when appropriate
Remove NR_EPSI and use std::numeric_limits<nr_double_t>::epsilon()
Use std::pair for pair

It allow to use efficient STL implementation
Simplify custom characteristic and operatingpoint class by using std:: class
Begin to simplify ptrlist by using STL
Use std::list as base of ptrlist

Simplify the code and allow to use well known pattern
use classical push_front/remove for children list

Less confusing to use well known construct
Simplify handling of name of environment using std::string

Less code duplication
Merge branch 'forguillem_cleanup_20141224'

Mainly cleanup and improvement.