Added logic to ImapFolder.GetSubfolders() to filter out unexpected folders
Added logic to ImapFolder.GetSubfolders() to filter out unexpected folders

This shouldn't be necessary, but broken IMAP servers like SmarterMail 13.0
(which is apparently not very smart at all) ruin it for the rest of us.

Fixes issue #149

mganss/MailKit,nachocove/MailKit,sstraus/MailKit,eino-makitalo/MailKit,matt2003/MailKit,jamie-dainton/MailKit,FubarDevelopment/MailKit,dsbenghe/MailKit,jstedfast/MailKit