[Dovecot] IMAP stress testing tool

[Timo Sirainen]

I updated my IMAP stress testing tool to support also APPENDs and print
some nice statistics. If you want to try for yourself, it's here:

http://dovecot.org/tools/imaptest.c

I thought about adding some more features in future to it, such as:

 - Add a header to each appended message containing MD5 sum of it. When
fetching, verify that the MD5 sum is valid.
 - Do randomized fetch requests (headers, size, flags, etc.)
 - Do randomized search requests
 - sort, thread