When a publishing uses a publish prefix, instead of listing the contents
of the whole bucket under the storage prefix, only list the contents of
the bucket under the storage prefix and publish prefix, and cache it by
publish prefix.
This speeds up publish operations under a prefix.
instead of caching the whole s3 bucket, cache only the pool path. this
requires an additional parameter, and since this is an interface, all
implementations need to follow. might help in other backends too.
closes#1181
This is related to #506
As a first step, don't pass MD5 explicitly, pass checksum info object,
so that as a next step we can choose which hash to use.
There should be no functional changes so far.
Next step: stop returning explicit paths from public package pool.