Fix: CatalogTraversal<> and GarbageCollector<> Unit Tests on 32bit

This fixes the `CatalogTraversal<>` and `GarbageCollector<>` unit tests under 32 bit operating systems. I was generating timestamps using `mktime()` with a full year notation. However, this functions requires "years since 1900". On 64 bit this is not a problem as `time_t` is 64 bit long, in contrast to 32 bit. Meh!