Fix current nightlies.

* Keep zinc + sbt branches synched.  We can't use stable sbt + unstable zinc for IDE/Scala builds.  Migrate to both stable.
* Create new build files for all unstable branches (to catch issues between inc. compiler changes + zinc
* Upgrade to dbuild 0.6.5.

Review by @harrah / @cunei 

cc> @retronym @adriaanm @gkossakowski @dragos - and sorry for the breakage.