Cache bucket content by prefix

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.

aptly/interfaces.go

@@ -70,7 +70,7 @@ type PublishedStorage interface {
 	// Remove removes single file under public path
 	Remove(path string) error
 	// LinkFromPool links package file from pool to dist's pool location
-	LinkFromPool(prefix string, path string, fileName string, sourcePool PackagePool, sourcePath string, sourceChecksums utils.ChecksumInfo, force bool) error
+	LinkFromPool(publishedPrefix, publishedRelPath, fileName string, sourcePool PackagePool, sourcePath string, sourceChecksums utils.ChecksumInfo, force bool) error
 	// Filelist returns list of files under prefix
 	Filelist(prefix string) ([]string, error)
 	// RenameFile renames (moves) file