Ok, I screwed up. When I put in cram-md5 and digest-md5, I left the alternative...

Ok, I screwed up.  When I put in cram-md5 and digest-md5, I left the alternative as being "plain", which is a misnomer.  There really IS a mechanism called "plain", and what we're doing isn't it.  So I've renamed our "plain" to "login".

For IMAP, it uses the IMAP4rev1 "LOGIN <user> <pass>" syntax.
For SMTP, it uses the AUTH LOGIN (two-step) method.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@4376 7612ce4b-ef26-0410-bec9-ea0150e637f0