Defaulting USE_PKG_ADMIN_DIGEST to yes

[Thomas Klausner <wiz%gatalith.at@localhost>]

Hi!

For switching away from CVS, joerg has prepared
USE_PKG_ADMIN_DIGEST=yes to compare file checksums using 'pkg_admin
digest' instead of using the RCS Ids for identifying when a package
needs to be rebuilt because the pkgsrc files have changed.

I think we can turn this on independent of the actual CVS migration,
and I'd like to do this soon.

Any comments?
 Thomas