Test suite: Add coverage for update_elf_closure

At present, the output is empty because there are
no resolved ELF dependencies.
update_elf_closure: Use some C++11 features
uodate_elf_closure: Use cxxll::pg_put_copy
update_elf_closure: Add self-dependencies for simpler joins
Manual: Add a reference to the Concepts chapter to the tutoral
Manual: Add a reference to the elf_closure table to the tutorial
Manual: Add elf_closure query to the tutorial