wrong error message when add-program's file not found

[Patrick Stevens]

In sextant.__main__, after the lines
        # in case of Python 2, where FileNotFoundError is undefined
        # note: ConnectionError subclasses IOError, so must come first

the following line should be
        logging.error('Input file {} was not found.'.format(args.input_file))
rather than
        logging.error('Input file {} was not found.'.format(args.input_file[0]))

Don't want to make this change myself so near to a demo.