Implemented the use of "Newton" as minimisation algorithm for R2eff curve fitting instead of simplex.
Running the test script: test_suite/shared_data/dispersion/Kjaergaard_et_al_2013/2_pre_run_r2eff.py
For 50 Monte-Carlo simulations, the time drop from: 3 minutes and 13 s, to 1 min an 5 seconds.
task #7822(https://gna.org/task/index.php?7822): Implement user function to estimate R2eff and associated errors for exponential curve fitting.
Authored by: tlinnet 2014-08-27
Parent: [r25333]
Child: [r25335]
