Remove unhelpful try/except blocks

In these cases, it seems better to let any lower-level exceptions
propagate up, so we have the full traceback to debug any problems.
Fix for shape bug in loading ASCII catalogs with only one row (#394)
Remove other places with the try-reraise pattern
(#394)
remove more try-except-raises in the des module
(#394)
Merge branch 'master' into #394
Merge pull request #398 from GalSim-developers/#394

#394 Fix bug for 1-line catalogs, and also remove try-except-raise pattern when not helpful