An unintrusive implementation - no existing interfaces changed, and a single addition for obtaining all of the different long names.
Notes:
* Tests added for the new functionality, and existing tests expanded to take it into account.
* It is now impossible to specify long names with commas in them (but then, that wasn't properly supported before either, more of an oversight).
* The multiple long options are not included in the usage information - just the first one of them is printed
