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
MockCatalog::root_hash with suffix
add scaffold for `cvmfs_swissknife gc`
TEST: scaffold for garbage collector test case
add a simple implementation of a HashFilter
TEST: basic test case for SimpleHashFilter
remove copy and paste garbage
add implementation of GarbageDetector
make all MockCatalogs directly accessible for the test cases
allow for counting objects in HashFilter
instrument SimpleHashFilter for testability
TEST: first simple garbage collection test case
TEST: T_GarbageCollector.PreserveLatestTwoRevisions
mv gc*.h garbage_detector*.h
add include guard around hash_filter.h
typedef for CatalogT in CatalogTraversal<>