Add support for tarbal-and-patch "TaP" repositories

These are repositories meant to support external packages, containing the
upstream tarball and patches (if any) that need to be applied to it.
Lots of work on x* verbs, TaP functionality
Removed all x* verbs; added "DEVMODE" (-e) switch instead
Documentation fixes
Renamed pkgbuild to eupspkg
bugfix: support tag files not in server root