The documented release process is to do npm run recompile, merge the
resulting branch to develop, and then do npm run relase, which does
not do another build.
This process should probably be changed, but for the moment ensure
that npm run recompile (as well as npm run package:beta) runs
buildTasks.checkinBuilt after each .build to preserve the old procedure.
You can now do npm run clean:buildDir, ... clean:releaseDir, or just
... clean, which does both.
The release directory is automatically cleaned before packaging
commences.
Make the destination directories for certain build/package/release
steps more easily (and centrally) configurable.
This only deals with building *_compressed* files;
blockly_uncompressed.js and the various msg/js/*.js files are not
affected by this commit.
