Added a source_repo_id to each revision, and repo_id to each
Source and Dest. The repo_ids include repository type
(cvs,p4,revml,vss,...) and the repo_server fields. Changed the
$self->...->set() and $self->...->get() lines in VCP::Dest::* to
pass in a conglomerated key value, by passing in the key as an
ARRAY ref. Also various restructuring in VCP::DB.pm,
VCP::DB_file.pm and VCP::DB_file::sdbm.pm related to this
change.