TEST: T_CatalogTraversal.ZeroLevelHistoryTraversal
rename MightPush() to Push()
directly track is_root of MockCatalog
FIX: MockCatalog::Clone()
FIX: initialization of RNG in MockCatalog
add doc of catalog count in MockCatalog revision
FIX: initialize global test state
TEST: add simple test cases for history traversal