Standalone CAPABILITY response

[emersion]

See emersion/go-imap#561

GMail does this:

T2 LOGIN "[email protected]" "password"
* CAPABILITY IMAP4rev1 CHILDREN UNSELECT LITERAL+ NAMESPACE XLIST UIDPLUS ENABLE ID IDLE MOVE
T2 OK LOGIN Completed.

Instead of this:

T2 LOGIN "[email protected]" "password"
T2 OK [CAPABILITY IMAP4rev1 CHILDREN UNSELECT LITERAL+ NAMESPACE XLIST UIDPLUS ENABLE ID IDLE MOVE] LOGIN Completed.

This behavior is problematic because the RFC says that once a LOGIN command has completed, the cached capabilities must be cleared by the client.

Offending implementation: imap.gmail.com