oldstable-proposed-updates based on COMMENTS directory

if section of source is different to binary section; restore
functionality on source-only overrides; croak if trying to set
priority of a source override; never set priority of source
overrides; correct typo in logging (s/priority/section/ at
one place)

so we don't get reminded at the start of each month. Thanks to
Random J.

This allows for more than two keyrings to be used.

Remove code to handle bug closures differently for NMUs or experimental uploads and just let version tracking sort it out instead.

[rmurray] change default compression scheme for both Sources and Packages to gzip and bzip2 rather than uncompressed and gzip (Packages) and gzip (Sources).  Use old defaults for proposed-updates.

[rmurray] BTS pseudo packages: drop install, installation, boot-floppy, slink-cd, potato-cd and nonus.debian.org.  Update base.