Avoid infinite loops

[ddundo]

There is a potential infinite while loop here:

PyGEM/pygem/bin/run/run_simulation.py

Lines 501 to 504 in ebddb98

	while not abs(np.median(calving_k_values) - calving_k) < 0.001:
	calving_k_values = calving_k + np.random.normal(loc=0, scale=calving_k_nmad, size=nsims)
	calving_k_values[calving_k_values < 0.001] = 0.001
	calving_k_values[calving_k_values > 5] = 5

This caused #58 to hang (i.e., the while loop was never broken).