[Dovecot] Compiler warnings in dovecot-2.1.2 and pigeonhole 0.3.0

I'm seeing a few warnings emitted when building for x86. They're pretty obvious, but if you want the configure options etc, I can provide those.

In Dovecot 2.1.2 (I also see some of these in 2.1.1):

1. src/lib-index/mail-cache-fields.c

(comparison between two last_used fields) mail-cache-fields.c: In function 'mail_cache_header_fields_read': mail-cache-fields.c:406: warning: comparison between signed and unsigned

2. src/director/user-directory.c

(comparison with ioloop_time) user-directory.c: In function 'user_directory_user_is_recently_updated': user-directory.c:147: warning: comparison between signed and unsigned

3. src/replication/replicator/replicator-brain.c

(comparison with ioloop_time) replicator-brain.c: In function 'doveadm_replicate': replicator-brain.c:113: warning: comparison between signed and unsigned

4. src/replication/replicator/replicator-queue.c

(comparison with ioloop_time) replicator-queue.c: In function 'replicator_queue_pop': replicator-queue.c:201: warning: comparison between signed and unsigned

In Pigeonhole 0.3.0:

5. src/managesieve-login/client-authenticate.c

(passing size_t * not uoff_t *) client-authenticate.c: In function 'managesieve_client_auth_read_response': client-authenticate.c:214: warning: passing argument 3 of 'i_stream_get_size' from incompatible pointer type