FIX: rename kAlgorithmIdentifier
factor out MockCatalog for code reuse
add mocked files to MockCatalog
add file chunk mocks to MockCatalog
add MockCatalog::ListReferencedObjects()
TEST: MockObjectFetcher can hide catalogs
dummy implementation of ObjectFetcher::FetchTagList()
typedef for CatalogT in CatalogTraversal<>
ignore 404 on historic root catalogs
documentation update
print error message for failed traversal
code cosmetics
silence error mesages in CatalogTraversal<>
TEST: CheckVisitedCatalogs() can ignore catalog count
TEST: make RevisionMap accessible by test cases
TEST: GetCatalog() to access random catalogs
TEST: CatalogTraversal<> can ignore 404 on root catalogs
TEST: check return value of Traverse()
FIX: ObjectFetcher checked wrong file path
improve logging of ObjectFetcher