DragonFly 3.4 branched, release candidate tagged

[Justin Sherrill]

DragonFly 3.4 is branched -  as a release candidate, with the current
target for 3.4.0 release as the weekend of April 13-14.

Note that in previous releases, we tagged "x.y.0" on branch, and
"x.y.1" on release.  I'm now tagging "x.y.0rc" for the release
candidate at branch time, and we'll tag with a more normal (to my
ears) "x.y.0" for the release.

If you build a 3.4.0rc image *right now*, you'll get an older
quarterly release of pkgsrc.  That'll be changed tomorrow as the
DragonFly pkgsrc git source is updated and I change where 3.4's
/usr/Makefile points.