Move stamps around; chroot login target; disable vanilla kbuild

- Rationalize some stamps:  put into /stamps/ directory
  - Need the rest in there, too
- Add <distro>/<arch>/chroot target to log into chroot
- Fix problem where linux-tools don't unpack a second time
- kernel-rt-deb2 submodule:  disable vanilla kernel build
- Print more diagnostics in pbuilderrc
  - Precise builds breaking on kernel build; not sure why