Bug in determining the segmentation stamp for the 2D spectra files.  Also add a "ymax" parameter to control the largest allowable thumbnail extractin.
Bug in determining the segmentation stamp for the 2D spectra files.  Also add a "ymax" parameter to control the largest allowable thumbnail extractin.

git-svn-id: b93d21f79df1f7407664ec6e512ac344bf52ef2a@882 f9184c78-529c-4a83-b317-4cf1064cc5e0

gbrammer/pygrism,gbrammer/unicorn,gbrammer/unicorn,gbrammer/pygrism