The only reference to MD5 there is about the SMTP server, not the IMAP....
However... the problem is that the 0.1.1 login function must have something wrong in it, at least if you have courier-imap as IMAP server. The result is Roundcube is deadly slow!
I copied the login function from 0.1-rc1 imap.inc and pasted it in the same file of the current version and I solved the problem: Roundcube is now fast as it should be!
Lukas