Modified systemtest Relax_disp.test_estimate_r2eff() to first do a Grid Search, then minimise and then estimate the errors for R2eff and i0.
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: [r25348]
Child: [r25350]
