The modelSize is the internal PIFF model grid size.  This gets
sent to the piff config rather than stampSize for the "size" entry.

modelSize defaults to 25. Update the stampSize to default to sqrt(2) * 25 ~ 35
to accomodate rotations

Add a check that stamp size is big enough

This is an important check when working in sky coords

Oddly at 45 degrees piff is giving a singlular matrix error
and fails to fit.  We should track this down before accepting
this PR.  135 works fine so I wonder if there is something
sepcial about 45 for this test

Will work for FITS wcs

We think its an issue with the underlying galsim code
rather than the wrapper