Find extra paths for default CA bundle trough the SSL module if possible (Python 3.4+)

[keithbowes]

For me at least, this changed from it from giving the message "ERROR: Default CA bundle was requested, but OfflineIMAP doesn't know any for your current operating system" to actually working.

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Additional information

Nothing really to add. I was a bit undecided about the route to take. It would make most sense to prefer getting the information through the SSL module, but I kept the dictionary first, as not to step on the toes of those who worked on that dictionary. I suppose an advantage of the route I took is that the behavior won't change for users who are using a known OS, but it will work in more OSes that aren't in the dictionary.