pkg_dry usage and updates

Antonio Huete Jimenez wrote up his experiences using pkg_dry on DragonFly, which were mostly successful.

He followed up with a script that takes care of the initial setup for pkg_dry, and noted that following pkg_dry in CVS is the best idea at this point, as it’s going through rapid development.

It should be possible to point pkg_dry at or one of the mirrors, and perform binary-only remote installs and upgrades of pkgsrc packages.