caldav: check for attendees before failing on bad organizer

(patch from Ken)
dbtool: fast output
buf_ensure: don't roundup the size until we know we need to
util: clarify MMAP handling for buf_*
cyrusdb: only CRC check if integrity checks turned on
twoskip: keep a separate location tracker for 'foreach'

Avoids a ton of strcmp work
twoskip: readahead in foreach to reduce lockyness
dbtool: use retry_writev for reliability
retry: don't copy the iovec until we know that writev was incomplete
twoskip: don't keep re-reading base and size pointers
twoskip: don't be confused by chained deletes

(they can't exist now, but maybe one day, and it doesn't cost much to check)
stitch: don't write past what we read
twoskip: use skipdelete in consistency/recovery stages
buf printer
mboxlist: adding of rights to self
dlist test - deep structure, numeric value
dlist: parsesax interface
mboxlist: use saxdlist parser for mboxlist entries
mboxlist: don't forget the ACL!
test: use util.h