Revert "Use oversampling=1 by default"

This reverts commit 1833aa076ab7878439fcd40c4610cf761d4afd6b.

Conflicts:
	galsim/optics.py
Fix bug in calculateStepK that sometimes greatly overestimates size (and thus underestimates stepk)
Update tests to be consistent with oversampling=1.5
Merge branch 'master' into #343