option passing bug

This is a minor bug fix for the last pull request.

in the last update i decided to pass the parse_obsoletes option through as an argument in each method. Unfortunatly i forgot to pass it for some calls... that resulted in only the first obsolete message beeing parsed, which was also not speced.

It was ugly enough at that time and would've got even more ugly now, so i added an option instance variable which holds all options. 

To make sure default options are used on consecutive calls if no options are set, current instance option variable gets merged with default options of the method on each call. Additionally all invalid options for a method will get dropped before the merge with the instance options.

multiple obsoletes is speced now, and i added specs for the option fallback.