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
Style improvements
Bug#3849 imap/arbitron.c: fix warning about uninitialized data

When the usage() function is not recognized as noreturn by clang,
the latter complains that month/day/year are unitialized, whenever
the condition on line 152 are true.

https://bugzilla.cyrusimap.org/show_bug.cgi?id=3849
One can not strcmp items that are not available.
[imap/mboxlist.c]: Do not free newmbentry for it is later used in updating mupdate
[imap/imapd.c]: Allow RENAME to specify a partition, or a server, or both.

Again, the third parameter to a RENAME is more like a location than a
partition or server.

When a RENAME is issued, the command is proxied for MBTYPE_REMOTE
mailboxes.

Specify 's!p' to both transfer a mailbox on to the partition p of
server s.

Specify 'p' to move the mailbox between partitions on the current
backend.

Specify 's', where 's' is an invalid partition name on the current
backend server, to have the backend treat the argument as a server
address.
Sieve Date Extension
sieve/sieve.y: fix compiler warnings
[timsieved]: Proxy using the original username, not the one with translated hierseps
imap/mboxevent.c: fix compiling, when mboxevent is disabled