let LookupTables extrapolate a small amount
(#569)
check for slop for equalSpaced True and False
(#569)
make SED.fphotons store the rest-frame spectrum, and redshift inside of __call__.
(#569)
SED.fphotons -> SED._rest_photons and simplify roundoff limit guards
(#569)
keep argMin() and argMax() the same, put slop in bounds check
(#569)
fix comments
(#569)
Wrap assert_raises tests in try block
(#569)
Merge pull request #575 from GalSim-developers/#569

#569 add small extrapolation tolerance to LookupTables