re-engineering notes

LruCache<> uses custom allocator and custom linked list --> make it STL with pool allocator
SmallHash<> has custom allocator --> use C++ STL conform allocator

download: proper abstraction of "network path"
namespaces: use anonymous namespaces more systematically, review use of namespace together with moving source files into subdirectories (name spaces reflect relative path)
Replace cvmfschecksum.$fqrn special format by manifest