get rid of args element in staged-scalac
Regularity for build.xml: 1 output dir / project

Untangle actors, msil builds from library/compiler builds.
For further regularity, always build java files.

TODO: update IDE projects
Preliminary support for zinc.

To use Zinc with the ant build:
  - install zinc and symlink the installed zinc script to ${basedir}/tools/zinc
    (${basedir} is where build.xml and the rest of your checkout resides)
  - make sure to set ZINC_OPTS to match ANT_OPTS!
  - invoke ant as `ant -Dstarr.version="2.10.1" -Dlocker.skip=1`
    (zinc does not work if locker is only classfiles, needs jars
     TODO rework the build to pack locker and build using that when using zinc?)

Mostly to enable dog fooding of incremental compilation work for now.
formatting
comments to address reviewer feedback
Merge pull request #2346 from adriaanm/build-zinc

Make build even more regular