add scaffold for `cvmfs_swissknife gc`
add SQL for listing all referenced hashes
add Catalog::GetReferencedHashes()
add Catalog::revision()
prototype implementation of real garbage collection
scaffold for `cvmfs_server gc`
TEST: utility functions for GC test cases
TEST: scaffold for basic GC integration test
FIX: AbstractUploader::Remove() didn't render suffix
TEST: extend 557 with chunked files
FIX: nested catalogs in GetReferencedObjects()
Catalog can be non-root without having a parent
TEST: 558 garbage collection with nested catalogs
ObjectFetcher::Fetch can handle arbitrary objects
add ObjectFetcher::FetchTagList logic
TEST: named tag aware garbage collection
garbage collection parameters
TEST: FIX: 557 and 558 - autotagging
TEST: disable debug for 557, 558 and 559
TEST: preserve some historic catalogs