SCons Bootstrap ReWrite

Here's what SCons' internal build should do:

1. build docs (if enabled)
2. build API docs (if docs enabled and api docs enabled)
3. build wheel and sdist_gztar
4. build scons-local zip and tgz package
5. expand packages so runtest.py can run against them? (is this still needed)

Files to be generated

• scons-$VERSION.tar.gz
• scons-$VERSION.zip
• scons-local-$VERSION.tar.gz
• scons-local-$VERSION.zip
• scons-src-$VERSION.tar.gz
• scons-src-$VERSION.zip
• scons-doc-$VERSION.tar.gz
• Announce.txt
• CHANGES.txt
• RELEASE.txt