Just because the corruption is a hundred years old, doesn't mean we should propagate it. O'Henry was known for his wordplay; he's also the author of several textbook examples to define irony, and not the kind Alanis sang about.
Did you look at the etymology at any of the sites google found? Granted, the internet is not an authoritative source, but of the top 10 hits, I only saw one that agrees with "cut muster".
Regardless of the origins of the phrase, after 100 years it's become part of the English language. The language evolves to reflect how it is spoken, whether we approve or not.