Bug #3839: Cyrus::IMAP does not use -cafile/-capath.

When calling Cyrus::IMAP authenticate with -capath and/or -cafile it fails to
pass them to _starttls when starttls is used but not for authentication.

authenticate also fails to translate CApath and CAfile to -capath and -cafile,
so if CApath or CAfile are passed to authenticate, they won't be used.
Make sure 'r' is initialized (it is set under conditionals and returned as the function return code)
imap_proxy.c: Fix handling of the backend returning large, large and arbitrary numbers for /freespace.
ctl_mboxlist.c: Prevent ctl_mboxlist from segfaulting on missing acl/part components
Do not push to / populate mupdate if the mbtype is deleted