this fixes #982 where files with fid >4294967295 were not considered for
garbage collection.

Refactors XrootCl.cpp to sanitise value returned by
`XrdCl::XRootDStatus::ToStr()`

[cta-admin] Corrected the showqueues command in the case ArchiveForUser and ArchiveForRepack exist for the same tapepool

This reverts commit b17463e8.