Fix galsim executable when installed by scons to actually work

bin/galsim.py

@@ -21,7 +21,7 @@
 """
 
 # Equivalent to python -m galsim ...
-import runpy
+import galsim.main
 
 if __name__ == '__main__':
-    runpy.run_module('galsim')
+    galsim.main.main()

galsim/__main__.py

@@ -19,7 +19,8 @@
 from .main import main
 
 if __name__ == '__main__':
-    # MJ: I didn't think the if __name__ == '__main__' thing was required inside of __main__.py,
-    # but without it, Python 3 runs main() twice.  I don't really understand why this is, so
-    # if someone has a better way to structure this code, I'm open to suggestions.
+    # The galsim executable will import this and then run main().
+    # So in that case, we don't want to also run main() here, since then it would run twice.
+    # However, `python -m galsim config.yaml` will run this as a program, so then we do want
+    # to call main.  Hence this `__name__ == '__main__'` block.
     main()

galsim/main.py

@@ -44,7 +44,7 @@ def parse_args():
         import argparse
 
         # Build the parser and add arguments
-        parser = argparse.ArgumentParser(description=description, add_help=True, epilog=epilog)
+        parser = argparse.ArgumentParser(prog='galsim', description=description, add_help=True, epilog=epilog)
         parser.add_argument('config_file', type=str, nargs='?', help='the configuration file')
         parser.add_argument(
             'variables', type=str, nargs='*',