[Dovecot] Apple patches 1-5

Here are the first few simple patches from Apple, based on
dovecot-1.1.7. The comments with "APPLE" in them helped us merge in
your new releases; feel free to remove them. Please let me know if
you want subsequent patches in a different format, or if you have any
questions.

Patch #1. Some versions of Mac OS X have buggy CMSG_* macros.

Patch #2. Don't set "<username>=1" in the environment.

Patch #3. Some versions of Mac OS X return near-duplicate kevents.

Patch #4. Null renames are actually pretty slow on HFS (Apple's file
system), so avoid them.

Patch #5. Required by Apple's lawyers.