[Dovecot] CATENATE doesn't support literal+ url

[Mike Abbott]

> Dovecot-2.2.1 does not appear to support URLs specified via non-synchronizing literals

Or synchronizing literals either:

b2 append inbox catenate (url {8}
b2 BAD Error in IMAP command APPEND: Invalid arguments.

Although the consequences of this are less severe since clients should send no more data for that command after receiving the tagged response.