Now that targets are serialized, introduce

Now that targets are serialized, introduce
two new convenience targets:

- update: svn update toplevel and try hard
          to locate updatable subdirectories
					using cunning tricks
- happiness: update then build and test

so what one wants to do now is:
  nice gmake --jobs happiness

Have fun!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47716 91177308-0d34-0410-b5e6-96231b3b80d8