add new head version
update version number (including in <storage_api> parameter) and publish/expire dates
allow dots in item names
forbid zero length item names
correct If-Unmodified-Since -> If-Match and If-Modified-Since -> If-None-Match
correct 409/304 response to 412 for If-Match and If-None-Match
reference RFC2616 for ETag, If-Match and If-None-Match headers