RHEL 5-era autoconf did not define these, so define them manually
when they are missing.

Define builddir as '.'  The scripts require this.  It won't work
in the srcdir != builddir case, but we don't care about that for
RHEL 5.

This commit also moves the builddir / abs_srcdir variable setting
above the include of subdir-rules.mk, in case that include uses
these variables.

Useful script:

  for f in $(find -name Makefile.am | xargs fgrep '$(abs_srcdir)' -l) ; do
    if ! grep -q '^abs_srcdir' $f; then
      echo missing in $f
    fi
  done

The two tarballs:

  8252 bytes   tests/data/filesanddirs-10M.tar.xz
 41152 bytes   tests/data/filesanddirs-100M.tar.xz

contain, as their names suggest, highly compressed files and
directories, with unpacked size respectively around 10M and 100M (the
precise size after unpacking depends on the filesystem).

These can be used for testing purposes.

Update all copyright dates to 2012.