Turning Dan Bron's comments into an answer:
It means damned. That profanity was considered unfit to print at the time.
This is very plausible to me, but there doesn't appear to be a written source for it. We might be unlikely to find one:
It’s not an abbreviation, it’s a redaction. 19th C authors were big on redaction (believe they thought it lent an air of authenticity). So you’re not going to find this spelled out in any dictionary, and any examples I can show you will have the same problem you currently have with your examples: the word is intentionally redacted, so we’re left to infer what it means from context. It’s not like the author is going to redact it and then leave a footnote saying “by this, I meant damned”.
I would imagine that someone probably documented this at some point (maybe in a 19th C style manual), but one would be hard-pressed to find it.