ignore hidden files in attachment directories too (consistent with ignoring hidden calendars, hidden calendar objects, etc)
ignore hidden files in attachment directories too (consistent with ignoring hidden calendars, hidden calendar objects, etc)

git-svn-id: 81e381228600e5752b80483efd2b45b26c451ea2@7775 e27351fd-9f3e-4f54-a53b-843176b1656c

trevor/calendarserver,trevor/calendarserver,trevor/calendarserver