Log Message:
Multiple fixes:
- Let the used user and group be customized through  SCREWS_USER and
  SCREW_GROUPS.
- Fix usage of PKG_USERS, which broke the build as seen in bulk build logs.
- Fix handling of configuration file (stale files could be left before in
  ${PREFIX}/etc).
- Honour VARBASE.
- Do not hardcode /usr/pkg in patches.
- Fix the "hsml" module so that it can find the lua library (missing \ 
rpaths).

Bump PKGREVISION to 3 due to all the previous changes.

Most of this brokenness was present since the package was first imported.
(Oh man, I hate packages reinventing the wheel when it comes to the build
infrastructure...  I'm sure it's still not clean enough.)