AC_MSG_RESULT was not used everywhere after AC_MSG_CHECKING.
Therefore two lines from configure output was mixed in some cases.

Detect directory with python libraries and add this
directory to the list of directories to be searched for linker.

Several parts of the HBAC python bindings did not work with old Python
versions, such as the one shipped in RHEL5.

The changes include:
* a compatibility wrapper around python set object
* PyModule_AddIntMacro compat macro
* Py_ssize_t compat definition
* Do not use PyUnicode_FromFormat
* several function prototypes and structures used to have "char
  arguments where they have "const char *" in recent versions.
  This caused compilation warnings this patch mitigates by using
  the discard_const hack on python 2.4

Also update BUILD.txt