Master dir and local workspace cannot be overridden, it doesn't actually make sense. Also changed a couple of variable names to make them more friendly.
Moved some logic to identify the dd-build location so that dd-raw.mk is now general purpose and the bootstrapping code for dd-build is in the Makefile for the dd-build project itself.
Added feature so that each build is identified with a revision identifier and then the Current link is set to the most recent build.