[CMake] building cmake without the bootstrap step

[René J.V. Bertin]

Never mind, this tweak to the bootstrap script should take care of anything not directly obvious. Could do with an automated test of the installed version but the accepted version range is so large that doesn't seem to be the trouble.

```
if [ -x ${cmake_prefix_dir}/bin/cmake ] ;then
  # use the existing cmake that we'll be replacing.
  ln -s ${cmake_prefix_dir}/bin/cmake ${cmake_bootstrap_dir}/cmake
else
  # Run make to build bootstrap cmake
  if [ "x${cmake_parallel_make}" != "x" ]; then
    ${cmake_make_processor} ${cmake_make_flags}
  else
    ${cmake_make_processor}
  fi
  RES=$?
  if [ "${RES}" -ne "0" ]; then
    cmake_error 9 "Problem while running ${cmake_make_processor}"
  fi
fi
cd "${cmake_binary_dir}"
```

R