Caveats:

* gr-howto-write-a-block must be checked out into it's own top-level
  working copy for build, otherwise automake will grab the depcomp,
  install-sh, etc. files from the parent directory, and not put them
  in the distribution tarball.

* Ubuntu's automake (at least) will copy config.guess and config.sub from
  Ubuntu's system directory, even if there is already one in the directory.
  You need to 'svn revert config.guess config.sub' after running bootstrap
  and before running configure.