* Some platforms do not use the POSIX exit code, but at least have the
  decency to give a textual report we can use in the test framework.
* Some totally fail to report this on their own. For those systems a
  work-around was implemented.

* The failure resulted from a change in treatment of clean targets in
  recent automake version.

* This way additional information is given to users of yaxt at
  configure time.

with inclusion of installable yaxt.h. Header yaxt.h is no longer available
in src directory. Library components must use xt headers directly.