Add try/except clauses around input string filename/eval completions.
(#523)
Trap eval-string SED specification NameErrors
(#523)
Unit test for SED initialization
(#523)
Make the error message when string fails both file name and eval test a bit more descriptive
(#523)
Implement a similar check that the function is valid for DistDeviate string parameters
(#523)
Cleaned up error messages and SED string input exceptions.
(#523)
Streamline checking of red_limit and blue_limit in Bandpass constructor
(#523)
Merge pull request #530 from GalSim-developers/#523

#523 Somewhat unhelpful Bandpass error messages