If the IMAP server does not send a PERMANETFLAGS resp-code, assume all flags permanent
If the IMAP server does not send a PERMANETFLAGS resp-code, assume all flags permanent

Fixes issue #140

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