Added a demonstration of why the Ishima and Torchia 2005 error formula is incorrect.
The script test_suite/shared_data/dispersion/error_testing/simulation.py has been added to simulate
the fixed relaxation time period error propagation. This produces the test_suite/shared_data/
dispersion/error_testing/error_plot.agr Grace graph. The formula, graph and a description has been
added to the relax manual explaining everything.