* Extend PREBUILD/POSTBUILD define values to support more than
one argument.
* Delay normalization of PREBUILD/POSTBUILD define values
until all arguments in the define values can be processed.
* Convert PREBUILD/POSTBUILD build define value arguments
that are WORKSPACE or PACKAGES_PATH relative paths to
absolute paths.
* Append -p PlatformFile, --conf=ConfDirectory, and build target
flags to command line used to execute PREBUILD/POSTBUILD
actions.
* Remove PrebuildScript and PostbuildScript fields from the
Build class and use Prebuild and Postbuild fields instead.