publish: add by-hash entries for skel and AppStream files

SkelIndex was the only index constructor not propagating acquireByHash,
so with -acquire-by-hash the Release file advertises Acquire-By-Hash: yes
while no by-hash/ entries exist for these files and apt gets a 404.

deb/index_files.go

@@ -397,11 +397,12 @@ func (files *indexFiles) SkelIndex(component, path string) *indexFile {
 		relativePath := filepath.Join(component, path)
 
 		file = &indexFile{
-			parent:       files,
-			discardable:  false,
-			compressable: false,
-			onlyGzip:     false,
-			relativePath: relativePath,
+			parent:        files,
+			discardable:   false,
+			compressable:  false,
+			onlyGzip:      false,
+			acquireByHash: files.acquireByHash,
+			relativePath:  relativePath,
 		}
 
 		files.indexes[key] = file

deb/publish_test.go

@@ -537,6 +537,19 @@ func (s *PublishedRepoSuite) TestPublishAppStreamMultipleComponents(c *C) {
 	c.Check(published, DeepEquals, contribContent)
 }
 
+func (s *PublishedRepoSuite) TestPublishAppStreamAcquireByHash(c *C) {
+	s.snapshot.AppStreamFiles = map[string]string{
+		"main/dep11/Components-amd64.yml.gz": s.importAppStreamFile(c, "Components-amd64.yml.gz", []byte("DEP-11 content\n")),
+	}
+
+	s.repo.AcquireByHash = true
+	err := s.repo.Publish(s.packagePool, s.provider, s.factory, &NullSigner{}, nil, false, "")
+	c.Assert(err, IsNil)
+
+	base := filepath.Join(s.publishedStorage.PublicPath(), "ppa/dists/squeeze")
+	c.Check(filepath.Join(base, "main/dep11/by-hash/SHA256"), PathExists)
+}
+
 func (s *PublishedRepoSuite) TestPublishNoSigner(c *C) {
 	err := s.repo.Publish(s.packagePool, s.provider, s.factory, nil, nil, false, "")
 	c.Assert(err, IsNil)