Added a script and log file for calculating the numerical gradient for an exponential curve.
This uses the data at http://thread.gmane.org/gmane.science.nmr.relax.devel/6807/focus=6840 and
calculates the gradient using the scipy.misc.derivative() function both at the minimum and at a
point away from the minimum. The values will be used to construct a unit test to check the C module
implementation.