Change FFT memory Error to Warning?

[sidneymau]

Currently, GalSim will throw an error if the requested FFT is too large (cf.

GalSim/galsim/gsobject.py

Lines 1970 to 1971 in 4c04a1e

	if Nk > self.gsparams.maximum_fft_size:
	raise GalSimFFTSizeError("drawFFT requires an FFT that is too large.", Nk)

).

The default value for this is quite low (something like 2GB) and this often results in many jobs crashing and hanging. Every time I configure this to be larger, I still end up finding some object that needs more memory resulting in another crash. It would be helpful for this to be changed into a warning rather than an error.