deprecate cvmfs_server list-tags
TEST: adapt integration test 520 list-tags -> tag -l
FIX: check repository existence in cvmfs_server tag
FIX: quotes in tag description
TEST: adapt test 520 to incorporate quotes
FIX: tagging nested catalogs
FIX: do not double-close a transaction
Refactor: factor out rollback condition
add SqlListRollbackTags()
add History::ListTagsAffectedByRollback()
TEST: amend rollback unit test
TEST: add T_History::ListTagsAffectedByRollback
Refactor: Move AddPadding() from ListTags to CommandTag
print deleted tags after rollback
TEST: amend 520 to fiddle with undo tags
disallow to alter undo tags
Merge pull request #598 from reneme/fix-tags

FIX: Various Minor Bugs and UX Quirks in New Tag Implementation