Use correct has_arg when parsing command line options with getopt_long

[scareything]

getopt_long takes an array of struct option to represent recognized command line options. struct option has a field has_arg which specifies whether or not the command line option has an associated argument; possible values are:

• no_argument: no argument to the option is expected
• required_argument: an argument to the option is required
• optional_argument: an argument to the option may be presented

We've been incorrectly setting this field to optional_argument in some cases when the intent was to make the command line option itself optional. This PR sets has_arg to required_argument where appropriate, and adds logic to ensure that required options are passed.

[dovholuknf]

lgtm