Automate a bunch of build problems

* automated the versionName and versionCode nonsense.
* write out the VERSION file while we're updating the AndroidManifest.xml
* dynamically pull in rootProject/private.properties to load in
  customized parameters without clobbering parallel, daemonized
  compilation
* added a release_check.sh script to check the existence of a
  private.properties file prior to compilation of a release
* added release_check as a Makefile target and dependency to release