introduce CatalogTraversal<>::ConstructorParams
allow for history traversal until certain threshold
REFACTOR: CatalogTraversal<> for unit-testability
adapt user code of CatalogTraversal<>
add scaffold for T_CatalogTraversal unittests
fill CatalogTraversal test framework
first catalog hierarchy
add revision to MockCatalog
build a full test catalog hierarchy
TEST: simple traversal of HEAD catalogs
check catalog traversal order
check for dangling catalogs during traversal
TEST: SimpleTraversalNoClose
FIX: merge conflicts
FIX: hash::Ramdomize() with optional seed or Prng
TEST: T_CatalogTraversal.ZeroLevelHistoryTraversal
rename MightPush() to Push()
directly track is_root of MockCatalog
FIX: MockCatalog::Clone()
FIX: initialization of RNG in MockCatalog