Importing app with NameError

[ptbrowne]

I launch my application with

gunicorn "my_app:create_app()"

In create_app(), if there is a NameError like if variable was not declared, I get an AppImportError which swallows the original exception. I think it would be useful to print the original exception when catching the NameError.

        exc_type, exc_value, exc_traceback = sys.exc_info()
        traceback.print_exception(exc_type, exc_value, exc_traceback,
                                  limit=3, file=sys.stdout)

Made a mini PR.

[benoitc]

applied. thanks!